feat: implement gRPC internal scoring service for low-latency score d…

[Killerjunior]

feat: implement gRPC internal scoring service for low-latency score delivery (#338)

Summary

Adds an optional gRPC sidecar service (ScoringService) providing low-latency score delivery (ScoreWallet and BatchScoreWallets) over HTTP/2 Protobuf framing while maintaining shared SQLite authentication, scope checking, and rate limiting with the REST API.

Linked issue(s)

Closes #338

Type of change

• Bug fix
• New feature
• Refactor / code quality
• Documentation
• CI / tooling
• Cross-repo change (affects shared contracts — see below)

What was tested

Automated unit and integration test suite covering field-by-field REST parity, metadata-based authentication (x-ledgerlens-api-key), scope enforcement (read:scores), streaming batch order, GRPC_MAX_BATCH_WALLETS limits, shared rate-limiting counters, error masking, and TLS defaults:

python -m pytest tests/test_grpc_scoring_service.py -v
python cli.py grpc-serve --port 50051