Function build_pcurve_on_surface_range 

pub fn build_pcurve_on_surface_range(
    surface: &NurbsSurface,
    curve: &NurbsCurve,
    edge_start: f64,
    edge_end: f64,
    forward: bool,
    tolerance: f64,
) -> Result<NurbsCurve, String>

fit_pcurve_on_surface_range for the callers that only need the curve: the fit is ACCEPTED or REFUSED on its bar (accept_fit), never returned off it.