- Fix OSRM client to use semicolons (not commas) for source/destination
indices in /table API requests. Commas caused "Query string malformed"
errors for any batch with more than one origin.
- Add error handling in poi_distance_calculator for unreachable routing
engines (OSRM/OTP). Connection failures now log an error and skip the
mode instead of crashing the entire Celery task.