feat(sources_filter): add filter events

- Added new filter events
- Toggles for country, type, source
- Event to clear filters

Author: fulleni

lib/headlines-feed/bloc/sources_filter_event.dart

@@ -1,22 +1,59 @@
 part of 'sources_filter_bloc.dart';
 
-/// {@template sources_filter_event}
-/// Base class for events related to fetching and managing source filters.
-/// {@endtemplate}
-sealed class SourcesFilterEvent extends Equatable {
-  /// {@macro sources_filter_event}
+abstract class SourcesFilterEvent extends Equatable {
   const SourcesFilterEvent();
 
   @override
-  List<Object> get props => [];
+  List<Object?> get props => [];
 }
 
-/// {@template sources_filter_requested}
-/// Event triggered to request the initial list of sources.
-/// {@endtemplate}
-final class SourcesFilterRequested extends SourcesFilterEvent {}
+class LoadSourceFilterData extends SourcesFilterEvent {
+  const LoadSourceFilterData({this.initialSelectedSources = const []});
 
-/// {@template sources_filter_load_more_requested}
-/// Event triggered to request the next page of sources for pagination.
-/// {@endtemplate}
-final class SourcesFilterLoadMoreRequested extends SourcesFilterEvent {}
+  final List<Source> initialSelectedSources;
+
+  @override
+  List<Object?> get props => [initialSelectedSources];
+}
+
+class CountryCapsuleToggled extends SourcesFilterEvent {
+  const CountryCapsuleToggled(this.countryIsoCode);
+
+  /// If countryIsoCode is empty, it implies "All Countries".
+  final String countryIsoCode;
+
+  @override
+  List<Object> get props => [countryIsoCode];
+}
+
+class AllSourceTypesCapsuleToggled extends SourcesFilterEvent {
+  const AllSourceTypesCapsuleToggled();
+}
+
+class SourceTypeCapsuleToggled extends SourcesFilterEvent {
+  const SourceTypeCapsuleToggled(this.sourceType);
+
+  final SourceType sourceType;
+
+  @override
+  List<Object> get props => [sourceType];
+}
+
+class SourceCheckboxToggled extends SourcesFilterEvent {
+  const SourceCheckboxToggled(this.sourceId, this.isSelected);
+
+  final String sourceId;
+  final bool isSelected;
+
+  @override
+  List<Object> get props => [sourceId, isSelected];
+}
+
+class ClearSourceFiltersRequested extends SourcesFilterEvent {
+  const ClearSourceFiltersRequested();
+}
+
+// Internal event - not part of public API, hence leading underscore
+class _FetchFilteredSourcesRequested extends SourcesFilterEvent {
+  const _FetchFilteredSourcesRequested();
+}