parseXY function
Parses an "x,y" coordinate string into a (double, double) tuple, or
returns null if the input is malformed.
Used by CLI adapters that accept coordinate flags like --at, --from,
--to. The associated error message format is the adapter's responsibility.
Implementation
(double, double)? parseXY(String raw) {
final parts = raw.split(',');
if (parts.length != 2) return null;
final x = double.tryParse(parts[0].trim());
final y = double.tryParse(parts[1].trim());
if (x == null || y == null) return null;
return (x, y);
}