Add grpc transport

[rustycl0ck]

As the title says, this PR adds support for providing gRPC as a transport. This can help in offloading the authentication and authorization parts to the transport, and thus should allow a wider range of options when considering remote hosting of MCP servers.
It also provides streaming support by default (because gRPC supports bidirectional streaming natively).

[Copilot]

Pull Request Overview

This PR adds support for gRPC as a transport for MCP servers, enabling offloading of authentication and authorization while providing extensive examples and tests.

• Adds generated proto files and updated gRPC service definitions
• Implements and tests the gRPC transport in server and client examples
• Updates module dependencies and documentation to support gRPC usage

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
transport/grpc/protogen/jsonrpc/jsonrpc_grpc.pb.go	Generated gRPC client/server code for JSONRPCService
transport/grpc/protogen/jsonrpc/jsonrpc.pb.go	Generated protocol buffer code for JSONRPC messages
transport/grpc/jsonrpc.proto	Defines the JSONRPCService and message schema
transport/grpc/grpc_test.go	Introduces tests for various gRPC server transport behaviors
transport/grpc/grpc.go	Implements gRPC transport including message conversions and stream handling
go.mod	Updates dependencies and Go version/toolchain requirements
examples/grpc_example/server/main.go	Example server configuration using the gRPC transport
examples/grpc_example/client/main.go	Example client demonstrating how to send and receive gRPC messages
examples/grpc_example/README.md	Updated documentation and usage instructions for the gRPC transport