Geocoder trips open after N consecutive Nominatim failures and skips ticks
for a cooldown, instead of grinding the whole batch 1 req/sec on every tick.
Adds tests for _coerce_payload (malformed JSON degrades to {_raw}) and
parse_raw tolerating a malformed payload.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
