feat(headlines): add similar headlines state

- Created state classes
- Initial, Loading, Loaded
- Empty and Error states added

Author: fulleni

lib/headline-details/bloc/similar_headlines_state.dart

@@ -0,0 +1,32 @@
+part of 'similar_headlines_bloc.dart';
+
+abstract class SimilarHeadlinesState extends Equatable {
+  const SimilarHeadlinesState();
+
+  @override
+  List<Object> get props => [];
+}
+
+class SimilarHeadlinesInitial extends SimilarHeadlinesState {}
+
+class SimilarHeadlinesLoading extends SimilarHeadlinesState {}
+
+class SimilarHeadlinesLoaded extends SimilarHeadlinesState {
+  const SimilarHeadlinesLoaded({required this.similarHeadlines});
+
+  final List<Headline> similarHeadlines;
+
+  @override
+  List<Object> get props => [similarHeadlines];
+}
+
+class SimilarHeadlinesEmpty extends SimilarHeadlinesState {}
+
+class SimilarHeadlinesError extends SimilarHeadlinesState {
+  const SimilarHeadlinesError({required this.message});
+
+  final String message;
+
+  @override
+  List<Object> get props => [message];
+}