Make clashing wave resolution randomized.

This commit changes two things; it allows multiple single waves to have
the same wave number, and it makes the wave selection procedure pick
randomly between multiple valid matches.

Effectively, this means that MobArena now picks randomly when clashing
recurrent waves _also_ clash on priority (rather than deferring the
decision to the arbitrary but deterministic nature of sorted sets), and
it also picks randomly between multiple single waves with the same wave
number (which was not possible before).

This should allow server owners to add variety into their wave setups
while maintaining a great deal of control over the randomness involved.
For instance, it's now possible to have wave 10 be a boss wave, but the
_actual_ boss wave is randomly picked between three different waves all
with wave number 10. Upgrade waves could be randomized as well. As for
randomized recurrent waves, perhaps instead of having potentially four
different mobs in the same wave, a setup could instead have two _pairs_
of mobs that are randomly selected for a different kind of randomness.

Closes #795

changelog.md

@@ -11,6 +11,10 @@ These changes will (most likely) be included in the next version.
 
 
 ## [Unreleased]
+### Changed
+- Recurrent waves can now be randomized. If two or more recurrent waves clash on wave number, frequency, _and_ priority, MobArena will now randomly pick between them. This should make it easier to create more varied and interesting wave setups without having to resort to only massively randomized default waves.
+- Single waves can now be randomized. If two or more single waves clash on wave number, MobArena will now randomly pick between them. This means it is now possible to make randomly selected bosses for boss waves, for instance.
+
 ### Fixed
 - MobArena no longer throws errors when handling block explosions on Minecraft 1.21.