Bug Fixes:
- Fixed items not stacking after being listed/delisted from market
- Fixed potential item loss when creating auctions
- Fixed duplicate purchase issues in player shops
- Fixed auction bid refund exploits
- Fixed collection box spam-clicking causing item duplication
- Fixed shop deletion conflicts during active purchases
- Fixed database synchronization issues with collection items
- Fixed expired listing cleanup and database bloat

Improvements:
- Added collection box size limit
- Added maximum bid limit
- Added protection against negative price exploits
- Prevented shop owners from purchasing their own items
- Improved transaction safety with automatic refunds on failures
- Enhanced database connection management
- Better error handling throughout the plugin