Refuse re-probing failures too fast: 500/429 failures get a 2h backoff,
other errors 30m (flapping relays/quota stops hammering ipinfo every pass,
passes every 30 min instead of 15). One-line summary per pass
(geo N/M · fail: rate×a server×b) replaces the per-pool error wall.
New env POOL_GEO_PROBE_DISABLED=1 turns the feature off.