Adds support for 1.21.5, bug fixes and more!

- Added support to 1.21.3!

- Fixed WorldLoadEvent not called for generated slime worlds
- Potential fix for deadlocking the main-thread
- Fixed NPE warning when the module fails to load
- Fixed SuperiorSkyblock loading before SlimeWorldManager, causing incorrect detection of whether SlimeWorldManager is loaded (#37)
- Fixed the module loading all worlds for each island instead of only generated ones
- Fix the module teleporting the player more than once to his island
- Fixed teleporting to island warps not loading the worlds if needed in case of LazyWorldsProvider (#41)
- Fixed detection of end worlds from their name (#42)
- Fixed the module trying to unload worlds that still have players inside (#44)