Obtain normal from NanoVDB's Level Set intersection (ZeroCrossing)

Hi all!

Is there any way to compute normal after intersecting ray in a level set grid in NanoVDB? OpenVDB's LevelSetRayIntersector provides a method called intersectsWS() which among other return values, provides you with the normal vector.

Thanks

Start with NanoVDB's Level Set intersection and ZeroCrossing entry points, then compare their behavior with OpenVDB's LevelSetRayIntersector::intersectsWS(), which the issue identifies as the reference API. Determine whether the intersection can expose a normal and document or implement that capability; done means callers can obtain a normal after a level-set ray intersection.

Written by the indexing model from the issue text.