Next-Gen-CustomEnderChest

Implemented a data locking system (DataLockManager) to prevent race conditions between player join/quit, auto-saves, admin commands, and inventory close events. This resolves all known issues related to data loss, item duplication, and data overwrites.

Fixed an issue where /cec open <player> would show stale data for online players by prioritizing the live cache over persistent storage.

Fixed a bug where changes made by an admin to an offline player's chest would not save correctly or would be overwritten upon the player's next login.

Fixed a server crash (IllegalArgumentException: size 0) that occurred when a player without any customec.level.* permissions joined the server.

Drop Support 1.20

Add lombok