Function register_volume_mesh 

pub fn register_volume_mesh(
    name: impl Into<String>,
    vertices: Vec<Vec3>,
    cells: Vec<[u32; 8]>,
) -> VolumeMeshHandle

Registers a generic volume mesh with polyscope.

Cells are stored as 8-index arrays. For tetrahedra, indices 4-7 should be u32::MAX.