fix: improve endgame clock and gameplay stability

pkg/kcp/kcp.go

@@ -213,6 +213,10 @@ func (k *KCP) State() int32 { return k.state }
 // IsDeadLink reports whether resends exceeded the dead link limit.
 func (k *KCP) IsDeadLink() bool { return k.state != 0 }
 
+// PendingSends reports segments waiting to be transmitted or acknowledged.
+// Callers must serialize access with other KCP operations.
+func (k *KCP) PendingSends() int { return len(k.sndQueue) + len(k.sndBuf) }
+
 func (k *KCP) moveBuf() {
 	for len(k.rcvBuf) > 0 {
 		seg := &k.rcvBuf[0]