allow nearest-neighbor voxel interpolation

[toloudis]

Use Case

"the option to toggle voxel interpolation like in napari" - voxels either blend/interpolate into their neighbors or they have hard edges.

Solution

A render setting toggle switch.
implementation: Volume Texture sampling switches from linear to nearest. There is part of one shader that will probably have to do some different math too (new uniform var to configure it).

[toloudis]

in single slice mode remove the random ray offset and see if it looks fine. if the shader can know it's a single slice mode then we can skip some of the interpolation or even write a new shader to handle things