M.R.U

• Added compatibility for 1.21.5.
• Migrated to modstitch
• Added RegistryUtils for sound event retrieval.
• Added RenderUtils for texture rendering and easing types.
• Added JSONUtils for simplified optional JsonObject retrieval with defaults.
• Updated fabric.mod.json with correct metadata and swapped out the fabric slug for fabric-api for clarity.

• Fixes mixin crashes for NeoForge. Apologies for the wait.

Fixes mixin issues.

• Updated to add support for 1.21.4.
• Removed deprecated unpacking API and datagen callbacks.