fix: 修复 #194 #196

bukkit/src/main/java/net/momirealms/craftengine/bukkit/plugin/network/PacketConsumers.java

@@ -2290,7 +2290,7 @@ public class PacketConsumers {
     private static BukkitNetworkManager.Handlers simpleAddEntityHandler(EntityPacketHandler handler) {
         return (user, event) -> {
             FriendlyByteBuf buf = event.getBuffer();
-            user.entityPacketHandlers().put(buf.readVarInt(), handler);
+            user.entityPacketHandlers().putIfAbsent(buf.readVarInt(), handler);
         };
     }
 }

server-mod/v1_21_5/src/main/resources/mixins.craftengine.json

@@ -6,7 +6,6 @@
   "target": "@env(DEFAULT)",
   "compatibilityLevel": "JAVA_21",
   "server": [
-    "BlocksMixin",
-    "ItemStackMixin"
+    "BlocksMixin"
   ]
 }