feat(feed): add silent loading state

- Added HeadlinesFeedLoadingSilently state
- Implemented buildWhen for silent loading

Author: fulleni

lib/headlines-feed/bloc/headlines_feed_bloc.dart

@@ -86,7 +86,7 @@ class HeadlinesFeedBloc extends Bloc<HeadlinesFeedEvent, HeadlinesFeedState> {
     if (state is HeadlinesFeedLoaded &&
         (state as HeadlinesFeedLoaded).hasMore) {
       final currentState = state as HeadlinesFeedLoaded;
-      emit(HeadlinesFeedLoading());
+      emit(HeadlinesFeedLoadingSilently());
       try {
         final response = await _headlinesRepository.getHeadlines(
           limit: _headlinesFetchLimit,

lib/headlines-feed/bloc/headlines_feed_state.dart

@@ -16,6 +16,15 @@ sealed class HeadlinesFeedState extends Equatable {
 /// {@endtemplate}
 final class HeadlinesFeedLoading extends HeadlinesFeedState {}
 
+/// {@template headlines_feed_loading}
+/// State indicating that the headlines feed is being loaded
+/// without a full screen loading widget being showed.
+/// 
+/// usefull for inifinity scrolling fetches beyonf the first one
+/// {@endtemplate}
+final class HeadlinesFeedLoadingSilently extends HeadlinesFeedState {}
+
+
 /// {@template headlines_feed_loaded}
 /// State indicating that the headlines feed has been loaded successfully,
 /// potentially with applied filters.

lib/headlines-feed/view/headlines_feed_page.dart

@@ -112,6 +112,8 @@ class _HeadlinesFeedViewState extends State<_HeadlinesFeedView> {
         ],
       ),
       body: BlocBuilder<HeadlinesFeedBloc, HeadlinesFeedState>(
+        buildWhen: (previous, current) =>
+            current is! HeadlinesFeedLoadingSilently,
         builder: (context, state) {
           switch (state) {
             case HeadlinesFeedLoading():
@@ -120,6 +122,10 @@ class _HeadlinesFeedViewState extends State<_HeadlinesFeedView> {
                 headline: 'Loading...',
                 subheadline: 'Fetching headlines',
               );
+            // this silentcase will never be reached
+            // it here just to fullfill the switch comprehensive check
+            case HeadlinesFeedLoadingSilently():
+              return const Placeholder();
             case HeadlinesFeedLoaded():
               return RefreshIndicator(
                 onRefresh: () async {