Add update checking

lib/domain/app/update_failure.dart

@@ -0,0 +1,22 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+import 'package:hiddify/core/locale/locale.dart';
+import 'package:hiddify/domain/failures.dart';
+
+part 'update_failure.freezed.dart';
+
+@freezed
+sealed class UpdateFailure with _$UpdateFailure, Failure {
+  const UpdateFailure._();
+
+  const factory UpdateFailure.unexpected([
+    Object? error,
+    StackTrace? stackTrace,
+  ]) = UpdateUnexpectedFailure;
+
+  @override
+  String present(TranslationsEn t) {
+    return switch (this) {
+      UpdateUnexpectedFailure() => t.failure.unexpected,
+    };
+  }
+}