quantile method
Implementation
double quantile(double p) {
if (_sorted.isEmpty) return double.nan;
if (p <= 0) return _sorted.firstOrNull ?? double.nan;
if (p >= 1) return _sorted.lastOrNull ?? double.nan;
final double idx = (_sorted.length - 1) * p;
final int i = idx.floor().clamp(0, _sorted.length - 1);
return _sorted[i];
}