Full rewrite: zero-handwritten-protobuf gRPC pipeline

[barakplasma]

Summary

• Rewrites all of fastgrpc/ from scratch — fixes the 5 root-cause bugs from the old implementation (wrong MethodType usage, stale temp-dir cache, broken route matching, bad reflection service names, missing body_field attribute)
• New pipeline: app.openapi() → proto_gen.py → compiler.py → grpc.aio server
• Route dispatch uses normalized operationId as the canonical key, bridging proto messages directly to FastAPI endpoint functions
• Dynamic servicer built with a handler factory (_make_rpc_handler) to avoid closure bugs
• SHA256-based stub cache survives restarts (stored in .fastgrpc_cache/)
• 23 tests, 0 skips, all green

New structure

fastgrpc/
├── proto_gen.py   # OpenAPI → proto3 string
├── compiler.py    # grpcio-tools protoc wrapper
├── bridge.py      # operation_id → FastAPI endpoint dispatch
├── service.py     # grpc.aio server + dynamic servicer factory
└── core.py        # FastGRPC class: lifespan hooks + stub caching

CI/CD

• CI runs tests on Python 3.10/3.11/3.12 on every push and PR
• PyPI publish triggers on v* tags via OIDC trusted publishing (no stored secrets needed)

Test Plan

• uv run pytest tests/ -v — 23 passed, 0 failed
• Verify CI passes on GitHub Actions
• Configure PyPI trusted publishing before first release tag