Partial rewrite of the plugin

• Enderchests are now serialized in the files.

• Enderchests are now cached, performance should be a lot better for big enderchests.

• Added a new config option, you can now block the losing of items, it will prevent users from opening their enderchest until they regain the correct permission. (enabled by default)

• New Usermap built-in, should work for geyser compat (even for offline player)

• Admins can now modify the enderchests using the exsee command

• Updated for 1.21 (tested only on 1.21.4, but should work fine for all 1.21)