A2a Channel Provider
Owns the gRPC channel to the A2A service and hands out stubs that already send the a2a-version header. Per-call auth metadata is added separately by A2aGrpcClient.
Owns the gRPC channel to the A2A service and hands out stubs that already send the a2a-version header. Per-call auth metadata is added separately by A2aGrpcClient.