static createArraySpan(arr) {
    if (!arr) return null;

    if (arr instanceof ArraySpan) return arr;
    else return new ArraySpan(arr);
  }
Creates an ArraySpan instance from the given array.
If the input is already an ArraySpan instance, it returns the input.
@static
@param {Array|ArraySpan|any} arr - The array or ArraySpan instance.
@returns {ArraySpan|null} A new ArraySpan instance or null if the input is falsy.