refactor: dedupe findmnt invocation in safe_cleanup_work_dir

The catch-all mount-cleanup block called findmnt twice (once as an
existence guard, once in the pipe). Consolidate to a single call
captured to a local, guard with -n test. No behavior change — same
mounts, same order, same lazy-unmount.

Left the explicit known-mount loop alone; it's a faster path for the
deterministic mkarchiso bind mounts, with findmnt as the catch-all
for anything else. Not parallel strategies, just fast path + fallback.

0 files changed, 0 insertions, 0 deletions