[Bug] When looping through _activeChunks instead of all chunks, chunks will sometimes only wake for 1 tick and then sleep immediately

[leftbones]

Reproduce the issue by pausing the simulation, placing some pixels, then stepping forward with T -- the chunks with the new pixels will wake up, but the very next tick they become inactive again even though their sleep timers are at 29

[leftbones]

Moving the code that removes sleeping chunks from _activeChunks to World.UpdateEnd() did reduce the problem, but it didn't fix it. I need to go back and study the chunk code and how chunks are woken and slept to understand why this is happening.