Fzzy Core 0.5.0+1.20.1

Update FzzyPort methods with some new registries and other new helper methods
Add VariantRegistry system, for easy creation of mobs with texture and bahavior variations.
Fix modifiers duplicating on player death.
Add fzzy_core:advancement Advancement Criterion, allowing advancements to be granted on other advancements being granted.
Added new data-driven default modifiers system. Default modifiers for any modifiable item can now be defined via datapack. Automatically synced to clients.