Feature
Stale review cleanup
Analyse open PRs that have gone quiet and get a recommendation for each.
A stale review is a Review whose PR is still open but has had no activity for 7 days or more. A stale review batch analyses many of them at once.
Each one gets a recommendation: ALREADY_RESOLVED, SAFE_TO_MERGE, NEEDS_WORK, NUDGE_AUTHOR or STILL_RELEVANT.