Added #

• PaymentResultPage: Displays payment success or failure, with reference or error message.
• onSuccess and onError callbacks support in MoolreCheckoutScreen.
• Custom MoolrePayButton with full checkout flow example and payment state handling.

Changed #

• MoolreCheckoutScreen now detects deep links and invokes callbacks.
• AppBar close button in checkout screen now triggers onError with USER_CANCELLED and exits correctly.

Fixed #

• Navigation bug: closing the WebView after payment now correctly returns to the previous screen (e.g., form or result screen).
• Test cleanup: removed obsolete flutter_moolre_platform_interface and flutter_moolre_method_channel.
• Removed broken test flutter_moolre_test.dart due to refactor and simplified plugin implementation.