TF-3267 Implement HTML attachment preview

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

@@ -0,0 +1,40 @@
+import 'package:core/presentation/state/failure.dart';
+import 'package:core/presentation/state/success.dart';
+import 'package:model/email/attachment.dart';
+
+class GettingHtmlContentFromAttachment extends LoadingState {
+  GettingHtmlContentFromAttachment({required this.attachment});
+
+  final Attachment attachment;
+
+  @override
+  List<Object?> get props => [attachment];
+}
+
+class GetHtmlContentFromAttachmentSuccess extends UIState {
+  GetHtmlContentFromAttachmentSuccess({
+    required this.sanitizedHtmlContent,
+    required this.htmlAttachmentTitle,
+    required this.attachment,
+  });
+
+  final String sanitizedHtmlContent;
+  final String htmlAttachmentTitle;
+  final Attachment attachment;
+
+  @override
+  List<Object?> get props => [
+    sanitizedHtmlContent,
+    htmlAttachmentTitle,
+    attachment,
+  ];
+}
+
+class GetHtmlContentFromAttachmentFailure extends FeatureFailure {
+  GetHtmlContentFromAttachmentFailure({super.exception, required this.attachment});
+
+  final Attachment attachment;
+
+  @override
+  List<Object?> get props => [attachment];
+}