[oscars-integration] Thread MutationContext through buitlin standard library objects

[shruti2522]

Stacked on #5478, this PR enforces threading MutationContext through all internal builtins, removing previous temporary fallbacks.

Key Changes:

• Removed *_in methods, temporary methods like JsObject::new_in are gone. Main methods (e.g., JsObject::new) have absorbed their signatures and now require the context.
• Removed Default for core objects: StandardConstructors, IntrinsicObjects and Intrinsics can no longer use Default::default(); they must be instantiated via uninit(mc)
• Macros (eg., boa_class) were updated to dynamically fetch context.gc_collector() without violating Rust's mutable borrowing rules.
• Signatures in the CLI, examples and tests were updated. Detached tests and macros temporarily use &unsafe { boa_gc::MutationContext::global() } to minimize immediate code breakage

[Copilot]

🟡 Changes recommended

There are multiple verified compilation/logic issues in the new MutationContext threading (notably several &&MutationContext argument mismatches and an incorrect in_with value in JSON compilation).

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR continues the oscars GC integration by threading a MutationContext/GC allocator handle through engine initialization, compilation, runtime environments, and several builtin/object construction paths, while adding an oscars_backend feature surface to boa_gc and boa_string.

Changes:

• Introduces boa_gc::GcContext and exposes it on Context (Context::alloc, Context::gc_collector) to centralize GC allocations and collector access.
• Threads MutationContext through bytecode compilation (ByteCompiler, FunctionCompiler) and multiple VM/module/script/builtin code paths, replacing many MutationContext::dummy() call sites.
• Adds oscars_backend feature wiring across crates (GC/string/engine), plus supporting glue (dummy/leaky WeakMap, Trace/Finalize adjustments, workflow branch triggers).

File summaries

File	Description
tests/macros/tests/gcd_callback.rs	Updates test to use MutationContext::global() and adjusts lint allowances.
tests/fuzz/Cargo.toml	Adds a patch override for boa_string when running fuzzing workspace standalone.
examples/src/bin/jstypedarray.rs	Updates example to use MutationContext::global() bridge.
examples/src/bin/derive.rs	Adds crate-level lint allowance.
core/string/src/tests.rs	Replaces assert!(.. == ..) with assert_eq! in builder tests.
core/string/src/lib.rs	Adds oscars_backend Trace/Finalize impls for JsString.
core/string/src/builder.rs	Refactors match-arm formatting and adds clippy allows in latin1 conversion path.
core/string/Cargo.toml	Adds optional oscars dependency and oscars_backend feature.
core/runtime/src/test262.rs	Adjusts downcast/clone flow for SharedArrayBuffer to match new borrow semantics.
core/runtime/src/microtask/tests.rs	Updates log cloning to deref through guard before cloning.
core/runtime/src/console/tests.rs	Updates log cloning + loosens table header substring assertions for output differences.
core/runtime/src/abort/mod.rs	Updates borrow/clone pattern for oscars backend guard types.
core/macros/src/lib.rs	Refactors derive_trace to avoid mutable-by-value argument and adjust implementation generation.
core/interner/src/sym.rs	Switches Sym to derive Trace and uses #[unsafe_ignore_trace] field attribute.
core/gc/src/trace.rs	Wraps custom_trace! bodies in unsafe {} blocks to satisfy unsafe-op linting.
core/gc/src/test/weak.rs	Updates Gc type annotation in size-of test for branded lifetime.
core/gc/src/pointers/weak_map.rs	Adds WeakMap::get_value convenience accessor.
core/gc/src/pointers/mutation_context.rs	Makes dummy() const and adds global() alias constructor.
core/gc/src/oscars_weak_map.rs	Adds dummy/leaky WeakMap for oscars_backend.
core/gc/src/lib.rs	Adds oscars backend re-exports, tracing macros, GcContext, and feature gating adjustments.
core/gc/src/context.rs	Introduces GcContext with collector access and allocation helper methods.
core/gc/src/cell.rs	Converts assertions to assert_eq!/assert_ne! for clearer diagnostics.
core/gc/Cargo.toml	Reworks feature flags for oscars backend and propagates feature flags to dependencies.
core/engine/src/vm/tests.rs	Disables a GC stress test under oscars_backend.
core/engine/src/vm/opcode/push/environment.rs	Threads GC allocator usage through env ops and replaces dummy allocations with context.alloc.
core/engine/src/vm/opcode/function.rs	Adds explicit type in closure to satisfy inference under new backend types.
core/engine/src/vm/opcode/await/mod.rs	Replaces dummy allocations with context.alloc and fixes capture cloning.
core/engine/src/vm/mod.rs	Makes Vm::new require a MutationContext to allocate initial codeblock.
core/engine/src/vm/inline_cache/mod.rs	Adds explicit Shape binding to satisfy type inference.
core/engine/src/vm/code_block.rs	Adds clippy allow for clone_on_copy.
core/engine/src/value/integer.rs	Converts equality assertions to assert_eq!/assert_ne!.
core/engine/src/value/inner/nan_boxed.rs	Adjusts raw pointer handling and imports for oscars backend compatibility.
core/engine/src/value/inner/legacy.rs	Refactors custom_trace! match to avoid matching on &this.
core/engine/src/value/equality.rs	Converts debug assert to debug_assert_eq!.
core/engine/src/script.rs	Switches script inner allocations to context.alloc and threads MutationContext into compilation.
core/engine/src/realm.rs	Requires MutationContext for realm creation and allocations.
core/engine/src/object/shape/unique_shape.rs	Adds _in variants and threads MutationContext through shape/weak-shape operations.
core/engine/src/object/shape/shared_shape/template.rs	Adds _in variants for template shape transitions and object creation.
core/engine/src/object/shape/shared_shape/mod.rs	Adds _in transition APIs and threads MutationContext through transitions/weak upgrades.
core/engine/src/object/shape/shared_shape/forward_transition.rs	Adds _in insertion helpers and updates weak allocation to use provided context.
core/engine/src/object/shape/root_shape.rs	Adds RootShape::new_in and routes default construction through global context.
core/engine/src/object/shape/mod.rs	Adds _in variants for transitions and routes old APIs through global context.
core/engine/src/object/mod.rs	Documents TypeId usage differences under oscars backend.
core/engine/src/object/jsobject.rs	Adds _in constructors and changes raw pointer APIs to untyped *const () for backend compatibility.
core/engine/src/object/builtins/jsweakset.rs	Uses context.gc_collector() to initialize weak set backing store.
core/engine/src/object/builtins/jsweakmap.rs	Uses context.gc_collector() to initialize weak map backing store.
core/engine/src/object/builtins/jstypedarray.rs	Updates doc example to use context.alloc.
core/engine/src/object/builtins/jspromise.rs	Uses context.alloc for state allocation; makes JsFuture cloneable.
core/engine/src/object/builtins/jsfunction.rs	Adds empty_intrinsic_function_in and routes old API via global context.
core/engine/src/native_function/mod.rs	Switches closure allocations to MutationContext::global() and adjusts downcast/clone with guard deref.
core/engine/src/native_function/continuation.rs	Switches coroutine allocations to MutationContext::global() and adjusts raw Gc conversions.
core/engine/src/module/synthetic.rs	Threads MutationContext into compilation; switches to context.alloc for codeblock allocation.
core/engine/src/module/source.rs	Threads MutationContext into compilation; switches to context.alloc for codeblock allocation.
core/engine/src/module/mod.rs	Switches module allocations and test data insertion to context.alloc; adjusts guard cloning.
core/engine/src/module/loader/mod.rs	Derives GC traits for module cache key used inside GC-traced structures.
core/engine/src/lib.rs	Adds clippy allowances expected under oscars backend (Gc becoming Copy, etc.).
core/engine/src/host_defined.rs	Relaxes Finalize bound on HostDefined.
core/engine/src/error/mod.rs	Updates downcast/clone patterns and custom_trace! match to match new backend semantics.
core/engine/src/environments/runtime/mod.rs	Threads MutationContext through environment stack pushes and updates allocation call sites.
core/engine/src/context/mod.rs	Adds Context.gc: GcContext, plus alloc/gc_collector; threads MC through realm/vm creation.
core/engine/src/context/intrinsics.rs	Removes Default reliance by introducing uninit(mc) constructors and threading MC through templates/constructors.
core/engine/src/bytecompiler/mod.rs	Adds McWrapper and stores MutationContext reference in compiler; threads it to nested compilers.
core/engine/src/bytecompiler/function.rs	Threads MC through FunctionCompiler::compile and uses it for codeblock allocation.
core/engine/src/bytecompiler/declarations.rs	Passes compiler MC into nested function compilation.
core/engine/src/bytecompiler/class.rs	Passes compiler MC into nested compilation and uses it for codeblock allocations.
core/engine/src/builtins/weak/weak_ref.rs	Uses context.gc_collector() for WeakGc operations and adjusts tests for oscars backend.
core/engine/src/builtins/weak_set/mod.rs	Uses context.gc_collector() and disables tests under oscars backend.
core/engine/src/builtins/weak_map/mod.rs	Uses context.gc_collector() + new WeakMap::get_value helper; disables tests under oscars backend.
core/engine/src/builtins/uri/mod.rs	Adds uninit_in(mc) and routes default via global context.
core/engine/src/builtins/set/ordered_set.rs	Refactors custom_trace! loop variable naming to avoid borrow issues.
core/engine/src/builtins/promise/mod.rs	Switches multiple allocations to context.alloc for promise state tracking.
core/engine/src/builtins/json/mod.rs	Threads MC into ByteCompiler creation and switches codeblock allocation to context.alloc.
core/engine/src/builtins/iterable/mod.rs	Adds uninit_in(mc) and routes default via global context.
core/engine/src/builtins/intl/locale/utils.rs	Adjusts downcast/clone to deref guard under oscars backend.
core/engine/src/builtins/intl/locale/mod.rs	Adjusts downcast/clone to deref guard under oscars backend.
core/engine/src/builtins/intl/list_format/mod.rs	Converts assert to assert_eq!.
core/engine/src/builtins/generator/mod.rs	Refactors custom_trace! match to avoid matching on &this.
core/engine/src/builtins/function/mod.rs	Threads MC into function compilation and updates environment stack calls.
core/engine/src/builtins/function/arguments.rs	Adjusts environment deref under oscars backend.
core/engine/src/builtins/finalization_registry/tests.rs	Disables miri tests under oscars backend.
core/engine/src/builtins/finalization_registry/mod.rs	Uses context.gc_collector() for weak refs/ephemerons and adjusts upgrade/value paths.
core/engine/src/builtins/eval/mod.rs	Threads MC into eval compilation and switches codeblock allocation to context.alloc.
core/engine/Cargo.toml	Adds oscars_backend feature mapping to GC/string crates.
core/engine/benches/full.rs	Updates benchmark realm creation to pass a MutationContext.
Cargo.toml	Adds typeid dependency and patches boa_string git source to local path.
Cargo.lock	Updates oscars git revision and adds new transitive deps (typeid, etc.).
.github/workflows/webassembly.yml	Adds dev/oscars-gc to workflow branch triggers.
.github/workflows/test262.yml	Adds dev/oscars-gc triggers and skips test262 job when targeting that base branch.
.github/workflows/rust.yml	Adds dev/oscars-gc to workflow branch triggers.
.github/workflows/pull_request.yml	Adds dev/oscars-gc to workflow branch triggers.

Review details

Suppressed comments (1)

core/engine/src/module/loader/mod.rs:294

• Deriving boa_gc::Trace for ModuleCacheKey will require PathBuf and ImportAttribute to implement Trace, but there doesn't appear to be a Trace impl for those types in the repo. Since these fields contain no GC pointers, mark them with #[unsafe_ignore_trace] so the derive doesn't require Trace bounds.

• Files reviewed: 89/90 changed files
• Comments generated: 9
• Review effort level: Lite

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