isRhombus property
Whether this is a rhombus
All four sides have equal length (and it's a parallelogram).
Implementation
bool get isRhombus {
if (!isParallelogram) return false;
final len = AB.length;
return (BC.length - len).abs() < _epsilon &&
(CD.length - len).abs() < _epsilon &&
(DA.length - len).abs() < _epsilon;
}