How can I add custom 3D models to NPCs?

Hey everyone, I hope you're doing well. I'm trying to add custom 3D models with animations to my Nikkit server, but I'm not sure how to do it. I'm reaching out here to see if anyone can provide guidance on implementing models, custom menus, and similar features like the servers on Cubecraft, The Hive, and Lifeboat. I see a lot of potential with custom 3D models and animations, but I haven't found detailed documentation on how to do it. Can anyone help me out?