update method
Implementation
Future<AppSettings> update(AppSettings Function(AppSettings) updater) async {
final current = await load();
final updated = updater(current);
await save(updated);
return updated;
}
Future<AppSettings> update(AppSettings Function(AppSettings) updater) async {
final current = await load();
final updated = updater(current);
await save(updated);
return updated;
}