feat(use_case): add gRPC transport for UseCaseService

[allmonday]

Summary

Add create_use_case_grpc_server() — a new transport dispatcher that exposes UseCaseService methods as unary gRPC RPCs over JSON.

• JSON-over-gRPC: No protobuf code generation needed. Request/response bodies are JSON-encoded bytes.
• Service mapping: Each UseCaseService becomes a gRPC service, each @query/@mutation method becomes a unary RPC
• FromContext: Injected from gRPC metadata
• Error mapping: Python exceptions → gRPC status codes (NOT_FOUND, INVALID_ARGUMENT, PERMISSION_DENIED, INTERNAL)
• Optional dep: pip install nexusx[grpc] (only grpcio>=1.60.0)

Usage

from nexusx import UseCaseAppConfig, create_use_case_grpc_server

server = create_use_case_grpc_server(
    UseCaseAppConfig(name="project", services=[UserService]),
    port=50051,
)
await server.start()

Client calls /UserService/list_users with JSON body {}, gets back {"result": [...]}.

Test plan

• 14 tests covering basic invocation, errors, FromContext, server lifecycle
• Full test suite passes (933 passed)
• Demo runs end-to-end (demo/use_case/grpc_demo.py)
• Lint passes

🤖 Generated with Claude Code