Support Nexo/ItemsAdder.

It's already 2026-it's about time we added support for creating interfaces via resource packs. We need to add basic features found in deluxemenus/zmenu, such as material IDs from Nexo/ItemsAdder (Nexo:Id). This would allow us to pass custom items to interfaces, such as those with textures, 3D models, etc.

Without this option, you can't create custom GUIs. This is a very significant oversight in the plugin.