Now, entity/global/location schedulers implement a generic run,
runDelayed, and runAtFixedRate methods that provide a ScheduledTask
value that can be used to interact with the scheduled task.
Add also an async task scheduler that implements the same methods,
except the delays/periods are in time and not ticks, as the scheduler
is independent of the server tick process.
Additionally, throw on some unimplemented APIs now.
Plugins must add "folia-supported: true" to their plugin.yml
otherwise the server will refuse to load them.
Since Folia is a major breakage for plugins, the vast majority
of plugins will not function correctly on Folia. To prevent
user confusion from this, we will refuse to load the plugin
and provide a log indicating why - which will be much
more helpful than some random error log caused by
a breakage.
