feat: Refactor code structure and optimize performance across multiple modules

mobile-apps/client-app/lib/features/notificatins/domain/notification_entity.dart

@@ -0,0 +1,41 @@
+enum NotificationType {
+  general,
+  invoice,
+  event,
+}
+
+class NotificationEntity{
+  final String id;
+  final String title;
+  final String body;
+  final NotificationType type;
+  final DateTime dateTime;
+  final bool isRead;
+
+  NotificationEntity({
+    required this.title,
+    required this.body,
+    required this.dateTime,
+    required this.id,
+    required this.type,
+    this.isRead = false,
+  });
+
+  NotificationEntity copyWith({
+    String? id,
+    String? title,
+    String? body,
+    NotificationType? type,
+    DateTime? dateTime,
+    bool? isRead,
+  }) {
+    return NotificationEntity(
+      id: id ?? this.id,
+      title: title ?? this.title,
+      body: body ?? this.body,
+      type: type ?? this.type,
+      dateTime: dateTime ?? this.dateTime,
+      isRead: isRead ?? this.isRead,
+    );
+  }
+}