Added 1.21.3 support
Changed superleashes.use to superleashes.unbreakable
Added superleashes.unbreakable.portal for portal usage
Added superleashes.unbreakable.teleport for player teleportation
You'll need to assign permissions using your chosen permissions handler since they're all false by default now
Documentation has been updated to reflect these changes

spigot 1.21 support!
please report any issues