Add in-memory screenshot generation for sprites and phash

[ghost]

Skips writing/reading to disk by encoding to bmp and routing the output to stdout. No performance difference over internal nvme storage, but quite a bit faster than nas storage. Somewhat simpler as well.

info from user in discord channel

[bnkai]

Update from the discord channel.
Using the build from this PR seemed to hang the generate process. The specific user used it for sprite generation
The info from the files it stopped/hang at doesnt show anything obvious (filenames reducted from ffprobe report)
message.txt
message(1).txt
Switching back to current dev he was able to continue generating past those files

Edit:
Tested a few times after merging with develop first, i can't seem to reproduce the above issue.

[ghost]

Update from the discord channel.
Using the build from this PR seemed to hang the generate process. The specific user used it for sprite generation
The info from the files it stopped/hang at doesnt show anything obvious (filenames reducted from ffprobe report)

I managed to reproduce. The way we were reading out stdout/stderr was susceptible to stalls when the buffers filled up too quickly. I tore out the code and just let os/exec handle it, which seems to work fine. I'll run a phash rebuild overnight to make sure there's no more stalls.

EDIT: No stalls when regenerating phash for all my scenes.