listNames method
Return base-names of all entries in dir.
Implementation
@override
Future<List<String>> listNames(String dir) async {
final prefix = dir.endsWith('/') ? dir : '$dir/';
return _store.keys
.where((k) => k.startsWith(prefix))
.map((k) => k.substring(prefix.length).split('/').first)
.toSet()
.toList();
}