operator == method
Exact == on the coordinates (stored values, CLAUDE.md): -0.0 and
0.0 are the same point, and a NaN coordinate equals nothing, itself
included. Only a dimension's offset carries a side in its sign, and is
compared with compareTo (DimensionParams.==, R-2).
Implementation
@override
bool operator ==(Object other) =>
other is FixedEnd && other.x == x && other.y == y;