test(push_notifications): improve PushNotificationPayload test

- Refactor test to use fixture data for consistency
- Update props test to reflect current model structure
- Enhance copyWith test to include additional fields
- Simplify import statement for core package

Author: fulleni

test/src/models/push_notifications/push_notification_payload_test.dart

@@ -1,42 +1,33 @@
-import 'package:core/src/models/push_notifications/push_notification_payload.dart';
+import 'package:core/core.dart';
 import 'package:test/test.dart';
 
 void main() {
   group('PushNotificationPayload', () {
-    const title = 'Breaking News';
-    const imageUrl = 'https://example.com/image.jpg';
-    const data = <String, dynamic>{
-      'contentType': 'headline',
-      'id': 'headline-123',
-    };
-
-    const payload = PushNotificationPayload(
-      title: title,
-      imageUrl: imageUrl,
-      data: data,
-    );
-
-    final json = <String, dynamic>{
-      'title': title,
-      'imageUrl': imageUrl,
-      'data': data,
-    };
+    // Use a fixture to ensure consistency and avoid manual setup.
+    final payload = inAppNotificationsFixturesData.first.payload;
+    final json = payload.toJson();
 
     test('supports value equality', () {
       // Arrange: Create another instance with the same values.
-      const anotherPayload = PushNotificationPayload(
-        title: title,
-        imageUrl: imageUrl,
-        data: data,
-      );
+      final anotherPayload = payload.copyWith();
 
       // Assert: The two instances should be equal.
       expect(payload, equals(anotherPayload));
     });
 
     test('props are correct', () {
       // Assert: The props list should contain all the fields.
-      expect(payload.props, equals([title, imageUrl, data]));
+      expect(
+        payload.props,
+        equals([
+          payload.title,
+          payload.notificationId,
+          payload.notificationType,
+          payload.contentType,
+          payload.contentId,
+          payload.imageUrl,
+        ]),
+      );
     });
 
     test('can be created from JSON', () {
@@ -58,17 +49,22 @@ void main() {
     test('copyWith creates a copy with updated values', () {
       // Arrange: Define the updated values.
       const newTitle = 'Updated News';
+      const newContentId = 'new-content-id';
 
       // Act: Create a copy with the updated values.
-      final copiedPayload = payload.copyWith(title: newTitle);
+      final copiedPayload = payload.copyWith(
+        title: newTitle,
+        contentId: newContentId,
+      );
 
       // Assert: The new instance should have the updated values.
       expect(copiedPayload.title, equals(newTitle));
-      expect(copiedPayload.imageUrl, equals(imageUrl));
-      expect(copiedPayload.data, equals(data));
+      expect(copiedPayload.contentId, equals(newContentId));
+      expect(copiedPayload.imageUrl, equals(payload.imageUrl));
+      expect(copiedPayload.notificationId, equals(payload.notificationId));
 
       // Assert: The original instance should remain unchanged.
-      expect(payload.title, equals(title));
+      expect(payload.title, isNot(equals(newTitle)));
     });
 
     test(