feat(account): implement available countries bloc

- Add AvailableCountriesBloc to handle fetching and managing available countries
- Include logic to sort countries by name in ascending order
- Handle loading, success, and failure states
- Support error handling for HTTP exceptions and unexpected errors

Author: fulleni

lib/account/bloc/available_countries_bloc.dart

@@ -0,0 +1,57 @@
+import 'dart:async';
+
+import 'package:bloc/bloc.dart';
+import 'package:core/core.dart';
+import 'package:data_repository/data_repository.dart';
+import 'package:equatable/equatable.dart';
+
+part 'available_countries_event.dart';
+part 'available_countries_state.dart';
+
+class AvailableCountriesBloc
+    extends Bloc<AvailableCountriesEvent, AvailableCountriesState> {
+  AvailableCountriesBloc({required DataRepository<Country> countriesRepository})
+    : _countriesRepository = countriesRepository,
+      super(const AvailableCountriesState()) {
+    on<FetchAvailableCountries>(_onFetchAvailableCountries);
+  }
+
+  final DataRepository<Country> _countriesRepository;
+
+  Future<void> _onFetchAvailableCountries(
+    FetchAvailableCountries event,
+    Emitter<AvailableCountriesState> emit,
+  ) async {
+    if (state.status == AvailableCountriesStatus.loading ||
+        state.status == AvailableCountriesStatus.success) {
+      return;
+    }
+    emit(state.copyWith(status: AvailableCountriesStatus.loading));
+    try {
+      final response = await _countriesRepository.readAll(
+        sort: [const SortOption('name', SortOrder.asc)],
+      );
+      emit(
+        state.copyWith(
+          status: AvailableCountriesStatus.success,
+          availableCountries: response.items,
+          clearError: true,
+        ),
+      );
+    } on HttpException catch (e) {
+      emit(
+        state.copyWith(
+          status: AvailableCountriesStatus.failure,
+          error: e.message,
+        ),
+      );
+    } catch (e) {
+      emit(
+        state.copyWith(
+          status: AvailableCountriesStatus.failure,
+          error: 'An unexpected error occurred while fetching countries.',
+        ),
+      );
+    }
+  }
+}