Make temporary cleanup nonfatal

[kiwigitops]

Fixes #303.

Temporary record directories are cleaned up in Monitor.protect's finally block. If that cleanup raises, the cleanup failure replaces the actual recording result, so a failure to remove perf.data can make an otherwise completed run fail.

This wraps automatic temp-directory cleanup in Monitor.try_with, logs a warning on failure, and still returns Deferred.unit from the finalizer. Explicit -working-directory paths are unchanged because those are not auto-cleaned.

Validated:

• git diff --check

[kiwigitops]

Quick follow-up on this small fix. The temp cleanup failure can still mask the real recording result, so this is still current from my side. Happy to adjust the warning path if needed.