Move disk cleanup out of the Windows Update loop:
- PS scripts: extract Invoke-DiskCleanup function, add -CleanupOnly switch
for standalone post-update cleanup pass.
- Python command: always pass -SkipCleanup:$true during WU loop; after
loop exits 0, run a separate -CleanupOnly invocation (skipped if
--skip-cleanup). Fails fast if cleanup-only returns nonzero.
- Tests: 3 new tests for cleanup-runs-after-loop, skip-cleanup suppresses
it, and cleanup-failure propagates as ClickException.
- ruff --fix: remove unused shutil import, sort imports, fix UP037/UP035.