Proper slime and honey intersection

The current implementation of slime/honey intersection looks good but is incorrect.

When intersecting honey and slime blocks, the ray intersects two surfaces in the same block ("at once") and then overlays the colors, which is technically wrong.

It should instead hit the slime surface, refract due to entering slime/honey and then hit the core in the next ray iteration. The ray would travel through slime/honey for some distance, which it doesn't do right now. A bit like entering water and then intersecting an underwater block, but with honey/slime.

Start by locating the slime/honey intersection and ray-iteration entry points, then compare their behavior with the water and underwater-block path described in the issue. Done means the ray first hits the slime surface, refracts into the slime/honey volume, and reaches the core on the next ray iteration without overlaying both surfaces at once.

Written by the indexing model from the issue text.