1. Approximation of derivative (by Taylor-series and by three points).
2. Some methods (Degree(), GetType(), D0(), D3(), DN()) are added.
3. Getting of subInterval's boundaries.
4. Algorithm for checking if 1st derivative is equal to zero is amended.
5. Cases are controlled when extrema or Project point do not exist.
6. GetNormal() function for gp_Vec2d was added.
7. Computing of Value, D0, D1, D2 and D3 for offset curves was changed.
8. Limitation of tolerance for derivative computing was added.
9. Methods for computing trihedron in singularity point are added.
10. Test tests/bugs/moddata_3/bug23706 is added.
11. Restriction on the LastParameter for visualization of 3-D curves. Calling PlotCurve(...) function for last interval.
12. LProp package is modified for tangent computing in singularity point (LProp_CLProps, LProp_SLProps).
13. Added test cases for issue.
Deleting bad test cases for this fix
Add a checking into files Geom_OffsetSurface.cxx, Geom_OffsetCurve.cxx, Geom2d_OffsetCurve.cxx , which try to make continuity of bspline surfaces and curves more than C0 to build offset.
Delete duplicate code and checkings
Prevent change of offset curve / surface when exception is raised due to attempt to set new C0 basis curve / surface
Added new QA command OCC23683. Added test case bugs/moddata_3/bug23683
Internal cache in classes implementing b-spline curves and surface in Geom and Geom2d packages is protected from possible concurrency by mutex (added as a class field in each instance).
