mcp: resolve comments

- remove unnecessary lock for sending channel
- add todo to refactor the bind method

Author: h9jiang

mcp/streamable_test.go

@@ -356,9 +356,7 @@ func TestServerTransportCleanup(t *testing.T) {
 	})
 
 	handler.onTransportDeletion = func(sessionID string) {
-		mu.Lock()
 		chans[sessionID] <- struct{}{}
-		mu.Unlock()
 	}
 
 	httpServer := httptest.NewServer(handler)

mcp/transport.go

@@ -122,6 +122,7 @@ func NewInMemoryTransports() (*InMemoryTransport, *InMemoryTransport) {
 }
 
 type binder[T handler, State any] interface {
+	// TODO(rfindley): the bind API has gotten too complicated. Simplify.
 	bind(Connection, *jsonrpc2.Connection, State, func()) T
 	disconnect(T)
 }