refactor(cargo): improve lock parse error context and remove dead null-guards

[a-oren]

Summary

• Add lock file path and error message to the parseCargoLockHashes catch block for descriptive diagnostics (per CONVENTIONS.md error-handling guidance).
• Remove dead hashMap null-guards in addTransitiveDeps and addDirectDeps — parseCargoLockHashes always returns a Map, so all three call sites now use consistent direct .get() access.
• Add a test covering the malformed Cargo.lock warning (asserts path + error detail in console.warn).

Testing

• npm test -- test/providers/rust_cargo.test.js — 74 passing.

Implements TC-5729

Summary by Sourcery

Improve Cargo.lock parsing diagnostics and simplify dependency hash handling.

Enhancements:

• Improve Cargo.lock parse warnings with the file path and underlying error details.
• Remove unnecessary null guards when retrieving Cargo dependency hashes.

Tests:

• Add coverage for malformed Cargo.lock warnings, including the path and error message.

[sourcery-ai]

Reviewer's Guide

The PR makes Cargo.lock parse failures actionable by reporting the file path and underlying parser error, adds regression coverage with a malformed lock fixture, and simplifies dependency hash lookups around the guaranteed Map return value.

Sequence diagram for Cargo.lock parse failure diagnostics

sequenceDiagram
    participant CargoProvider
    participant CargoLockParser
    participant Console
    CargoProvider->>CargoLockParser: parseCargoLockHashes(manifestDir, opts)
    CargoLockParser-->>CargoProvider: Map or parse error
    alt malformed Cargo.lock
        CargoLockParser->>Console: console.warn(lockPath, error.message)
        CargoLockParser-->>CargoProvider: hashMap
        CargoProvider->>CargoProvider: Generate SBOM without hashes
    end

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Flow diagram for Cargo dependency hash lookup

flowchart LR
    Parse["parseCargoLockHashes returns Map"] --> Direct["addDirectDeps calls hashMap.get()"]
    Parse --> Transitive["addTransitiveDeps calls hashMap.get()"]
    Direct --> SBOM["sbom.addDependency with hashes"]
    Transitive --> SBOM

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File-Level Changes

Change	Details	Files
Improves malformed Cargo.lock diagnostics by including the lock file path and parser error detail in the warning while preserving hash parsing fallback behavior.	Expands the parse failure warning with the lock path, error message, and explicit no-hashes consequence. Adds a malformed lock fixture and verifies the warning contains the expected path, error context, and fallback text.	src/providers/rust_cargo.js test/providers/rust_cargo.test.js test/providers/tst_manifests/cargo/cargo_malformed_lock_test/Cargo.lock test/providers/tst_manifests/cargo/cargo_malformed_lock_test/Cargo.toml test/providers/tst_manifests/cargo/cargo_malformed_lock_test/cargo_metadata.json
Removes redundant null checks from dependency hash lookups based on the invariant that lock hash parsing always returns a Map.	Uses direct Map.get() access for transitive and direct dependency hash resolution. Keeps dependency generation behavior unchanged when a package has no matching hash.	src/providers/rust_cargo.js

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[sourcery-ai]

Hey - I've reviewed your changes and they look great!

Sourcery assessment

Approved.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.45%. Comparing base (b77d624) to head (7c42c0c).

Files with missing lines	Patch %	Lines
src/providers/rust_cargo.js	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #622   +/-   ##
=======================================
  Coverage   91.45%   91.45%           
=======================================
  Files          44       44           
  Lines       10172    10172           
  Branches     1840     1838    -2     
=======================================
  Hits         9303     9303           
  Misses        869      869           

Flag	Coverage Δ
unit-tests	91.45% <66.66%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/providers/rust_cargo.js	97.37% <66.66%> (ø)

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[Strum355]

I would personally remove the malformed lock test. Feels like a case of Claude being overzealous with adding tests for the tiniest things

[sourcery-ai]

Sourcery assessment

Approved.