feat(mc): init 1.21 support

Due to Paper ItemStack internal system change, we have wrap SlimefunItemStack. this may cause some problems.
See also: PaperMC/Paper#10852

src/main/java/me/mrCookieSlime/CSCoreLibPlugin/general/Inventory/ChestMenu.java

@@ -127,9 +127,17 @@ public ChestMenu addPlayerInventoryClickHandler(MenuClickHandler handler) {
      * @return The ChestMenu Instance
      */
     public ChestMenu addItem(int slot, ItemStack item) {
+        // do shallow copy due to Paper ItemStack system change
+        // See also: https://github.com/PaperMC/Paper/pull/10852
+        ItemStack clone = item == null ? null : new ItemStack(item.getType(), item.getAmount());
+
+        if (clone != null && item.hasItemMeta()) {
+            clone.setItemMeta(item.getItemMeta());
+        }
+
         setSize((int) (Math.max(getSize(), Math.ceil((slot + 1) / 9d) * 9)));
-        this.items.set(slot, item);
-        this.inventory.setItem(slot, item);
+        this.items.set(slot, clone);
+        this.inventory.setItem(slot, clone);
         return this;
     }