Shared Inventory + Hearts

Added new team system and synchronization features.

Changes:
- Added /inv teams commands.
- Players can now create and join separate inventory teams.
- Each team has its own shared inventory.
- Added optional shared hearts synchronization with /inv hearts true/false.
- Knockback is now synchronized automatically when shared hearts are enabled.
- Added /inv synchronize inv true/false to enable or disable inventory synchronization.
- Fixed several respawn/death issues with shared hearts.
- Fixed item duplication when multiple teammates die with the same shared inventory.