Remove dangling temporary directories from outputs/tensors at startup time

[lstein]

Summary

If the web app exits unexpectedly it may not run its shutdown routine, which removes temporary directories, among other things. At initialization time, this PR checks the base directories used by ObjectSerializerDisk for temporary directories left dangling from previous runs, and removes them.

Related Issues / Discussions

See #6242 for background on a bug that led to a large number of dangling temporary directories in outputs/tensors.

QA Instructions

If you have been running earlier versions of invokeai-web you probably have a lot of dangling temporary directories in outputs/tensors. When you run this PR, these directories should be removed.

Merge Plan

Merge when approved.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)

[psychedelicious]

My first thought is this should instead be the responsibility of the service that writes the files

[lstein]

My first thought is this should instead be the responsibility of the service that writes the files

Good idea. I'll modify the PR.

[lstein]

@psychedelicious The dangling tmpfile cleanup code has been moved into object_serializer_disk.py. When I did this I discovered many dangling tmp directories in outputs/conditioning as well as outputs/tensors, so this was a good move.

[psychedelicious]

Thanks! I did a bit of tidying. There was a logic bug - start() is only called after init, so this would actually delete the tmp dir that was created for the current session. I moved the logic around to handle this.

Also, we shouldn't delete files when ephemeral=False, so I handled that.

Added tests.