Important Fix for server side performace

• Reduced the memory usage of checking player's current slot detection.
• The system won't keep ticking the inventory changed detection when opening chest (This is the core issue why this is happening!!!)
• Btw, tip for inputting Spear weapon into slot: Just try to distant yourself and the anvil for a bit, and try click on the slots! Or you can quick switch while left clicking. This problem only exist after a few snapshots in 1.21.11 and it's certainly not my problem.

This fix should greatly improve the server performance. If needed, I will try to further optimize the system.