feat(types): expose language_code in SyncTranscriptResponse and auth_time_ms in DictationResponse

[pylrn]

Summary

Surfaces two response fields returned by AssemblyAI's synchronous transcription and dictation services that were previously omitted from the Node SDK TypeScript types:

1. language_code?: string in SyncTranscriptResponse:
   The sync transcription backend returns an ISO 639-1 language_code in the JSON response (e.g. "en", "es"). Exposing it allows callers to inspect which language the model detected or transcribed in, especially when language_codes was not explicitly provided in the request configuration. (Parity with Python SDK PR #257).

2. auth_time_ms?: number in DictationResponse:
   The Dictation API returns auth_time_ms as the authentication and API key validation portion of request_time_ms. While request_time_ms and sync_time_ms were already typed, auth_time_ms was omitted. (Parity with Python SDK PR #263).

Both fields are optional (undefined when absent) to preserve backwards compatibility with responses from older deployments.

Changes

• src/types/sync/index.ts: Add language_code?: string; to SyncTranscriptResponse
• src/types/dictation/index.ts: Add auth_time_ms?: number; to DictationResponse
• tests/unit/sync.test.ts: Add unit tests for language_code presence and omission
• tests/unit/dictation.test.ts: Add unit tests for auth_time_ms presence and omission
• CLAUDE.md: Update DictationResponse breakdown documentation
• package.json: Bump version 4.41.5 → 4.41.6 for version bump check
• CHANGELOG.md: Add [4.41.6] entry

Testing

• Unit tests: pnpm test:unit tests/unit/sync.test.ts tests/unit/dictation.test.ts tests/unit/exports.test.ts (113/113 passing)
• Lint & types: pnpm lint (eslint, tsc, prettier format, publint) all clean
• Build: pnpm build creates all distribution bundles cleanly