gridStep static method
A "nice" grid step for a max value, chosen on a log-magnitude basis so
ticks land on 1/2/5 multiples. Mirrors the Compose calculateGridStep.
Implementation
static double gridStep(double maxValue) {
if (!(maxValue > 0) || !maxValue.isFinite) return 1;
final magnitude = (math.log(maxValue) / math.ln10).floorToDouble();
final base = math.pow(10, magnitude).toDouble();
if (maxValue / base > 5) return base * 2;
if (maxValue / base > 2) return base;
return base / 2;
}