refactor: add ConnectivityService to handle network connections

lib/services/connectivity_service.dart

@@ -0,0 +1,26 @@
+import 'package:connectivity_plus/connectivity_plus.dart';
+
+class NetworkException implements Exception {
+  String message;
+
+  NetworkException({this.message = "Network state is offline!"});
+
+  @override
+  String toString() => message;
+}
+
+abstract interface class IConnectivityService {
+  Future<bool> isOffline();
+}
+
+class ConnectivityService implements IConnectivityService {
+  final Connectivity connectivity = Connectivity();
+
+  ConnectivityService();
+
+  @override
+  Future<bool> isOffline() async {
+    ConnectivityResult result = await connectivity.checkConnectivity();
+    return result == ConnectivityResult.none;
+  }
+}