Parallel pause images comparison

[Avasam]

Is your feature request related to a problem? Please describe.
A lot of people (myself included) would like to be able to use AutoSplit to estimate load removal during runs. (see #139 (comment), #232 and many messages on Discord)
I think this can be included before a complete rewrite for parallel split images (#36)

Describe the solution you'd like
I'd like to scope this feature separately from the main comparison loop as much as possible. Both to reduce potential breakage (#216) and reduce the added complexity as much as possible.

• The user would specify a special "pause images" folder (just like the splits folder)
• Support the comparison method flags
  Option A:
• Only the {p} (pause) and {b} (below) flags would be considered
• Maybe flag some images as "pause", some as "unpause" and AutoSplit tracks which state it's in? This may help with more complex cases
  Option B:
• No flags needed, just hit the pause toggle whenever any image is matched, or all are unmatched
  • This is exactly like Unload. It makes sense to not do more than current automated post-run tools can do anyway.

Performance concerns:

• We NEED to make sure we're re-using the frame obtained from the capture method.
• The whole load detection feature obviously will run in parallel
• How many images can we compare in parallel? Let the user decide? Can we use multiple CPU cores? (Improve asynchronous operations / Use observer pattern #219)
  • Most of the time, this will be a no-match, because the runner isn't in a loading screen (and that's when we need the most performance for other splits), so comparing sequentially to stop early on a match wouldn't help.

Describe alternatives you've considered
Alternative 1: Run 2 instances of AutoSplit with different images folders
Alternative 2: Interleave load images with the {p} (pause) and {bp} (below + pause) flags. But this makes it impossible to loop.

Additional context
For post-run or even for leaderboard load removals, I'd instead recommend a tool that can be re-run by verifiers as many times as they want in a robust manner. Even if AutoSplit supported it. See https://github.com/milankarman/Unload