Arc segments with extremely large radius compared to chord length can
cause floating-point precision issues in simulation. This change
introduces ARC_LINEARIZATION_THRESHOLD to treat such arcs as linear,
improving numerical stability in the simulator.
The following g-code was causing erractic behavior in the simulator due
to large-radius arcs:
```
G2 I88775.835760 J-1936991.545892 K0.000000 X102.063107 Y100.102815 Z12.700001
```
src/Mod/CAM/PathSimulator/AppGL/MillPathSegment.cpp:
- Added ARC_LINEARIZATION_THRESHOLD constant
- Updated arc motion detection to treat large-radius arcs as linear
- Improved handling of arc vs. linear segment classification
650ebf693e