Avoid the tinny audio pause while using rewind

[[Unknown]]

Rewind snapshots are handled kinda differently, i.e.:

1. Currently, no screenshot is captured, which avoids a GPU perf penalty. Files come with a screenshot.

2. The state is compressed differently. Rewind uses a base (uncompressed) screenshot every X states, and delta compresses by block for the non-base states. Files use Snappy to compress the one state in isolation.

3. Rewind snapshots are stored in a ringbuffer, to avoid reallocating memory. Files reallocate each time.

4. Files rename and swap with the old state and try to handle disk full. Rewind snapshots ignore all this.

The "core" of it is still the same, though. It's just that files have more wrapped around them, basically.

As for the pause - for me, the last change helped, and I made another change which reduces CPU burn in states more. Unfortunately, I was still able to notice a hiccup or two - differently not a whole half second or anything, I'd say more like a tenth of a second or something. Still bad, but I'm not sure what's causing it.

-[Unknown]