Stress Testing about beat-off HOT 2 CLOSED

As far as hits/patterns, there needs to be a mutex to prevent them from being removed while a render is happening.

This is mostly a problem for hits, which can be removed (they end) on update calls, which are called outside the main thread.

It'd be great to keep our 1000 fps output performance (or at least ~120 fps), but mutexes will definitely slow this down.

from beat-off.

Worked fine running for ~2.5 hours, although there was no tracking of memory usage/leaks. Noted problems:

• AGCs seemed to get a little wonky by the end. Probably some math error?
• Hits can segfault
• The full hit sometimes doesn't terminate.
  (These should all be treated as separate bugs)

from beat-off.