feat(distance): add Distance API support

Add full Distance API support matching the PHP SDK implementation:

- Add Coordinate class for flexible coordinate input formats (string, tuple, dict)
- Add distance() method for single origin to multiple destinations (GET)
- Add distance_matrix() method for multiple origins × destinations (POST)
- Add async job methods for large distance matrix calculations:
  - create_distance_matrix_job()
  - distance_matrix_job_status()
  - distance_matrix_jobs()
  - get_distance_matrix_job_results()
  - download_distance_matrix_job()
  - delete_distance_matrix_job()
- Enhance geocode() and reverse() with distance parameters
- Add type-safe constants for mode, units, ordering, and sorting
- Add verify_ssl parameter to client for testing with self-signed certs
- Add comprehensive unit tests and E2E tests
- Update README with full Distance API documentation

All changes are backward compatible - existing code continues to work.

Author: sylvesterdamgaard