When the upstream commit hash of the claimed upstream tag has not changed
since the last successful verify, reuse the cached file list instead of
re-cloning and re-hashing from scratch. This makes the canonical preflight
fast on the common case where upstream didn't move.
Cache is stored in .redbear-fork-verify/<fork>-<tag>.fingerprint. Touched
only after a successful full content diff, so cache corruption is detected
on the next run (commit hash mismatch triggers fresh clone).
vasilito
79285e4ebf