nextDelay method
Implementation
@override
Duration nextDelay(int attempt) {
if (attempt <= 0) return Duration.zero;
final int exponential = (baseMillis * pow(2, attempt - 1)).toInt();
final int capped = min(exponential, maxMillis);
if (capped <= 0) return Duration.zero;
final int half = capped ~/ 2;
final int jitter = half + _rnd.nextInt(half + 1);
return Duration(milliseconds: jitter);
}