feat(sdk): align request errors, retry delays and client cloning

[moonyue-w]

Summary

Align TypeScript request-error classification, retry-delay boundaries, and client cloning with the pinned Anthropic sdk-v0.127.0 baseline.

• Make connection failures, timeouts, and user cancellation inherit from APIError, preserving existing constructors and causes. HTTP status/header metadata remains absent on non-HTTP errors.
• Honor only positive retry delays within the single-timer limit; invalid, zero, negative, and oversized values use exponential backoff. Align millisecond-header precedence without changing retry eligibility.
• Add withOptions() to derive a client of the same concrete type, preserving unspecified settings, credentials, custom fetch, middleware, and the resolved base URL. Supplied client-level headers, query defaults, and middleware replace the corresponding option.
• Update resumable-stream classification, conformance tests, public types, README, changelog, and generated API documentation.

Why

Allow a single APIError catch to cover request failures, prevent oversized delays from becoming immediate retries, and make configuration reuse consistent across clients.

Verification

• npm run build: CommonJS and ESM build passed.
• npm run typecheck: passed, including derived-client and error-subclass types.
• npm test: 3,375 passed.
• npm run docs:check: passed; 26 README TypeScript snippets compiled.
• Standalone examples were not rerun; example files are unchanged and README examples were typechecked.
• Live integration runs are not required for these changes: existing live suites use maxRetries: 0; controlled transport tests exercise retry timing, error classification, and derived-client configuration.

Impact

• Public behavior/API changes recorded under Unreleased.
• CommonJS, ESM, and subpath exports remain covered by build/type tests.
• Generated API documentation and contract tests updated. Endpoint and wire-field fixtures are unchanged.
• Cross-SDK behavior considered; QCA retry safety rules retained.
• Migration notes included; no credentials, environment files, logs, or test output committed.

Breaking change: instanceof APIError now includes connection, timeout, and cancellation errors. Guard optional status and headers, and handle APIUserAbortError first when cancellation needs separate treatment. Existing HTTP-specific subclasses retain their typed metadata.