Enhance cache determinism and implement error serialization for remote workers

[lshariprasad]

This PR improves distributed build efficiency by standardizing cache outputs and enabling cross-process error replaying.

To-Do / Progress List
[x] Normalize Cache Metadata: Zero out mtimes and sort dependencies to ensure deterministic cache hashes.

[x] Implement Error Serialization: Added read/write methods to ErrorInfo for transmitting errors between worker and coordinator.

[x] Sync Parallel Workers: Updated worker protocol to replay import errors and maintain state consistency.

[x] Update Node Serialization: Fixed binary serialization for FuncDef and Var flags (e.g., is_generator, is_final).

[x] Refine Parser & MyPyC: Switched C-string encoding to hex and fixed module-level type: ignore logic.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅