Pruning used to only run at the end of a successful PropagationGridWorker
pass, so a stretch of failed compute jobs (k8s OOM kills, SIGTERM)
stopped prune from running and let the table accumulate ~5h of stale
rows. A dedicated PropagationPruneWorker now runs every 15 minutes on
its own Oban cron, and PropagationGridWorker also calls prune_old_scores
at the start of each run as a second safety net. Bumped the delete
timeout from 2m to 5m so the first catch-up pass has enough headroom.
Graham McIntire
664f1353db