Add a ray types example

[natevm]

We really need an example demonstrating how to use ray types, (which are different from visibility flags)

A quirk with the existing API seems to be that we require a context be made before requesting the number of ray types to use, but simultaneously we need the number of ray types set before a context can be made... So that API should really change to be more similar to gprtRequestNumRayTypes that gets called before the context is made.