Discrepancy of point and derivatives for SymbolicCubicBezier

[asteinh]

With the reparametrization of SymbolicCubicBezier to the arc length, point(s) now maps [0,1] linearly to [0, arc_length]. The derivatives computed from the composite path of the SymbolicPath class, however, don't take this reparametrization into account. The derivative of a path in a cubic Bezier segment at a certain point will therefore not correspond to the point.

[asteinh]

Taking the reparametrization into account when building the composite path significantly increases computation times...

[asteinh]

With 7cfda7a the natural parametrization is optional (and deactivated by default) - enable via SymbolicPath.natural_parametrization() (disable with argument False). Couldn't find another solution without increasing computation times unacceptably...