- 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.