Improve safety for Arb4, always use stricter safety for triangles and quadrilaterals

This MR improves the safety of the Arb4, which could be significantly wrong before for cases outside of the z range.

Additionally, we noticed that the safety for triangles and quadrilaterals can be too low (below 35%), so we now enforce the more rigorous calculation. A new variable -safety_ratio is added to the test raytracer, which throws and error if the safety ratio is worse than the provided value. The default is 0, so the option is switched off.