anchor.diff:   *
    * For long lists, this implementation can be considerably
    * more space- and time-efficient than the default [List] implementation.
  + *
  + * Integers stored in the list are truncated to their low 64 bits,
  + * interpreted as an unsigned 64-bit integer with values in the
  + * range 0 to 18446744073709551616.
    */
   abstract class Uint64List implements List<int>, TypedData {
     /**
  
positive.code:    * and copies over the elements.
     *
     * Values are truncated to fit in the list when they are copied,
     * the same way `operator[]` truncates values.
     */
    external factory Int64List.fromList(List<int> elements);
  
  
negative.code:    * and copies over the elements.
     *
     * Values are truncated to fit in the list when they are copied,
     * the same way storing values truncates them.
     */
    external factory Uint64List.fromList(List<int> elements);
  
  