Add functionality for custom NBT tags in ItemBuilder

A new method `addPersistentValue` has been added to the ItemBuilder class, allowing for the addition of custom NBT tags to items. This provides more flexibility in item customization.

bukkit/src/main/java/it/mycraft/powerlib/bukkit/item/ItemBuilder.java

@@ -83,6 +83,18 @@ public ItemBuilder setMaterial(Material material) {
         return this;
     }
 
+    /**
+     * Adds a custom NBT tag to the item
+     *
+     * @param type  The PersistentDataType
+     * @param key   The key
+     * @param value The value
+     */
+    public <V> ItemBuilder addPersistentValue(PersistentDataType<?, V> type, String key, V value) {
+        NBT.put(key, new Pair<>(type, value));
+        return this;
+    }
+
     /**
      * Sets the item's material getting it from a String
      *