Merge upstream/main into main

Resolve conflict in handlers_stage.go: keep lock-free packet
building pattern (copy session list, release lock, then build)
over upstream's in-lock QueueSendMHF approach.

Fix test compilation: remove objectIDs field references after
upstream removed it from Server struct.

Resync vendor directory with updated go.mod dependencies.

server/channelserver/handlers.go

@@ -337,7 +337,6 @@ func logoutPlayer(s *Session) {
 	s.server.Lock()
 	delete(s.server.sessions, s.rawConn)
 	s.rawConn.Close()
-	delete(s.server.objectIDs, s)
 	s.server.Unlock()
 
 	// Stage cleanup