feat(content_management): add archived headlines events

- Add LoadArchivedHeadlinesRequested event to request loading of archived headlines
- Add RestoreHeadlineRequested event to restore an archived headline
- Add DeleteHeadlineForeverRequested event to permanently delete an archived headline
- Update ArchivedHeadlinesEvent props to allow nullable objects

Author: fulleni

lib/content_management/bloc/archived_headlines/archived_headlines_event.dart

@@ -4,5 +4,36 @@ sealed class ArchivedHeadlinesEvent extends Equatable {
   const ArchivedHeadlinesEvent();
 
   @override
-  List<Object> get props => [];
+  List<Object?> get props => [];
+}
+
+/// Event to request loading of archived headlines.
+final class LoadArchivedHeadlinesRequested extends ArchivedHeadlinesEvent {
+  const LoadArchivedHeadlinesRequested({this.startAfterId, this.limit});
+
+  final String? startAfterId;
+  final int? limit;
+
+  @override
+  List<Object?> get props => [startAfterId, limit];
+}
+
+/// Event to restore an archived headline.
+final class RestoreHeadlineRequested extends ArchivedHeadlinesEvent {
+  const RestoreHeadlineRequested(this.id);
+
+  final String id;
+
+  @override
+  List<Object?> get props => [id];
+}
+
+/// Event to permanently delete an archived headline.
+final class DeleteHeadlineForeverRequested extends ArchivedHeadlinesEvent {
+  const DeleteHeadlineForeverRequested(this.id);
+
+  final String id;
+
+  @override
+  List<Object?> get props => [id];
 }