Version 2.1 Update

New Features:
- Villager Naming - Rename villagers using an anvil
- Trade Preview GUI - Shift + right-click in air to see villager info

Compatibility:
- Added 1.21.11 NMS support
- Updated Paper API to 1.21.1
- Updated Java requirement to 21

Fixes:
- Fixed update checker to use Bukkit scheduler instead of raw threads
- Removed unused database methods
- Fixed particle and enchantment API for 1.21

Trade Preview:
- Only works for employed villagers (not unemployed/nitwit)
- Requires shift + right-click in air
- GUI shows profession block and villager level
- Items cannot be taken from the preview GUI