v0.20.1

Tooling: pydoclint docstring gate

Adopts pydoclint with the same Google-style configuration as vgi-python, enforcing that documented arguments/attributes stay in sync with the code. Now runs in the CI lint job and is step 3 of the pre-commit checklist.

Docstring fixes (reviewed, not blindly frozen)

• Corrected genuine drift in HttpServerCapabilities, RpcMethodInfo, and ServiceDescription (missing / mis-ordered attributes).
• Documented Args on the public surface: RpcServer.serve_one, StreamSession.exchange, ShmAllocator.free, OutputCollector.merge_data_metadata, and the fmt_* debug helpers.
• Added class-level annotations to HttpTransientError (status_code / retry_after), resolving the attribute mismatch and improving type visibility.

No public API changes — docstrings, annotations, and dev tooling only.

Full diff: v0.20.0...v0.20.1