Remove systems from unloaded mods #20
Description
#14 introduces hot-reloading for mods and unloading. But the implementation simply deactivates outdated systems and registers new ones, which could begin to negatively affect performance after a while.
bevyengine/bevy#20298 introduces an api that allows removing systems from schedules by their sets. Since #21 wasvy injects each system into the world using a SystemIdentifier SystemSet. If these were tracked during setup, it could be possible to remove them once a new version of a mod is loaded.