Update to version 1.0.4 with improvements for commune resolution and API consistency

- Bumped the plugin version to 1.0.4 and updated the stable tag in the readme.
- Enhanced commune resolution in the ShippingMethod class for checkouts using ISO 3166-2 region codes, ensuring accurate handling of commune names.
- Prevented overwriting of destination state/country fields during AJAX updates.
- Added ISO 3166-2 region-code detection and expanded inline documentation for better clarity on Chile region vs commune handling.
