from<N extends num>  static method 
Implementation
static ScaleNum? from<N extends num>(Iterable<N>? list) {
  if (list == null || list.isEmpty) return null;
  num min = list.first;
  var max = min;
  for (var n in list) {
    if (n < min) {
      min = n;
    }
    if (n > max) {
      max = n;
    }
  }
  return ScaleNum(min, max);
}