Add domain layer for GetEmailContent

lib/features/email/domain/state/get_email_content_state.dart

@@ -0,0 +1,20 @@
+import 'package:core/core.dart';
+import 'package:model/email/email_content.dart';
+
+class GetEmailContentSuccess extends UIState {
+  final EmailContent? emailContent;
+
+  GetEmailContentSuccess(this.emailContent);
+
+  @override
+  List<Object?> get props => [emailContent];
+}
+
+class GetEmailContentFailure extends FeatureFailure {
+  final exception;
+
+  GetEmailContentFailure(this.exception);
+
+  @override
+  List<Object> get props => [exception];
+}