generateSecurePassword static method
生成包含大小写字母和数字的8位密码
Implementation
static String generateSecurePassword({int length = 16}) {
  final secureRandom = Random.secure();
  final allChars = '$_lowerCase$_upperCase$_numbers';
  // 确保至少包含一个数字和一个字母
  final passwordChars = [
    _getRandomChar(_lowerCase + _upperCase, secureRandom),
    _getRandomChar(_numbers, secureRandom),
  ];
  // 填充剩余6个字符
  for (var i = 2; i < length; i++) {
    passwordChars.add(_getRandomChar(allChars, secureRandom));
  }
  // 打乱顺序并组合
  return _shuffle(passwordChars, secureRandom).join();
}