[CAM] VCarve improvements

[phaseloop]

Rework of Vcarve operation to include features mostly available in commercial software of this kind. Those features are used to drastically improve carved surface quality (especially on smaller and less rigid CNC machines) and increase carving speed up to 50%.

1. Step down - carve in small increments (similar to other CAM operations). Each depth steps are grouped by surface to limit X/Y movements.
2. Finishing pass - run last path again (with optional offset) to remove fuzzy skin and/or other imperfections
3. Head movement optimization - do not lift and reposition head (G0 command) if start of next edge is withing 0.5 mm XY distance. This makes whole operation at least 50% faster with negligible loss of edge precision.
4. debugVoronoi method to render all voronoi paths used in path generation for debugging purposes.

Discussion and photo examples:

https://forum.freecad.org/viewtopic.php?t=87475

[sliptonic]

This looks good to me. Please disable the debug for production merge

[phaseloop]

This looks good to me. Please disable the debug for production merge

Fixed - thanks!

(edited previous comment: Did some benchmarking with cProfile and Path.Log.debug() stack parsing it may not be such a big issue after all).

Added a new commit with simple _caller() caching to have at least slight performance improvement that will be merged into FreeCAD 1.0:

4abafa1