Expose ON_NurbsCurve::ConvertSpanToBezier to Rhino3dm

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requested: https://discourse.mcneel.com/t/what-is-the-reason-why-nurbs-cannot-be-converted-to-bezier/150358

opennurbs: .h: https://github.com/mcneel/opennurbs/blob/f3687d492eb3c688665b3631851e182ce721e5c1/opennurbs_nurbscurve.h#L1086 .cpp: https://github.com/mcneel/opennurbs/blob/f3687d492eb3c688665b3631851e182ce721e5c1/opennurbs_nurbscurve.cpp#L2356

cs: https://github.com/mcneel/rhino3dm/blob/main/src/dotnet/opennurbs/opennurbs_nurbscurve.cs#L1051-L1058

js/py: .h: https://github.com/mcneel/rhino3dm/blob/main/src/bindings/bnd_nurbscurve.h .cpp: https://github.com/mcneel/rhino3dm/blob/main/src/bindings/bnd_nurbscurve.cpp

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Tested in js and py.