Create random alphanumeric string

gen_random_alphanum.dart

/// Courtesy of https://stackoverflow.com/a/61929967/10670707
Future<String> genRandomAlphanumeric(int length) async {
  const _chars = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz1234567890';
  Random _rnd = Random();
  return String.fromCharCodes(
    Iterable.generate(
      length,
      (_) => _chars.codeUnitAt(_rnd.nextInt(_chars.length))
    )
  );
}