Mystery item implementation

Zennysoft.Game.Ma.Implementation/Item/InventoryItem.cs

@@ -19,6 +19,8 @@ public abstract partial class InventoryItem : Node3D
   public abstract double ThrowDamage { get; }
   [Save("inventory_item_throw_speed")]
   public abstract float ThrowSpeed { get; }
+  [Save("inventory_item_tag")]
+  public abstract ItemTag ItemTag { get; }
 
   public abstract Texture2D GetTexture();
 }