Introduce a new napcat-rpc package implementing a deep-proxy RPC system. Adds client (createDeepProxy, proxy helpers), server (RpcServer, createRpcServer), serializer (serialize/deserialize, callback registry), and transport layers (LocalTransport, MessageTransport, message server handler), plus an easy API (createRpcPair, mockRemote, createServer, createClient). Includes TypeScript types, tsconfig and package.json. Wire-up: add package alias in napcat-schema vite config and add napcat-rpc dependency to napcat-test along with comprehensive rpc tests.
