feat(dependencies): add rxdart package and improve string extension methods for better handling of empty strings and gender parsing

test/features/chat/models/payment_model_test.dart

@@ -0,0 +1,25 @@
+import 'package:eatvio_app/features/chat/models/payment_model.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('PaymentModel', () {
+    test('создает PaymentModel с правильными значениями', () {
+      final model = PaymentModel(
+        paymentUrl: 'https://example.com/payment',
+      );
+
+      expect(model.paymentUrl, 'https://example.com/payment');
+    });
+
+    test('fromJson создает PaymentModel из JSON', () {
+      final json = {
+        'checkout_url': 'https://example.com/payment',
+      };
+
+      final model = PaymentModel.fromJson(json);
+
+      expect(model.paymentUrl, 'https://example.com/payment');
+    });
+  });
+}
+