Allow Ray.extinction_min_depth to be equal to 1

[vsnever]

There is a check in ray.extinction_min_depth.setter that prevents setting it to 1: https://github.com/raysect/source/blob/3c1f2f2f1cce9c2a2d5ca2952a70af3287d53dbf/raysect/optical/ray.pyx#L276-L279

Because of this, ray.max_depth cannot be set to 1 either: https://github.com/raysect/source/blob/3c1f2f2f1cce9c2a2d5ca2952a70af3287d53dbf/raysect/optical/ray.pyx#L291-L294

However, setting both values to 1 will be the easiest way to run the simulation without reflections. For now, the only alternative to this is to replace all reflective materials with AbsorbingSurface().

Is there a reason why ray.extinction_min_depth or ray.max_depth cannot be equal to 1?