[FEAT] Support mesh-grid source data

[MikeSWang]

Is the requested feature related to an issue?

No.

Summary

Currently the only source data type supported is catalogues of discrete particles with positions and weights. An additional source data type is mesh grids of sampled density fields with lines of sight given by the grid position vector.

Alternatives

N/A

Implementation

Overload existing field operation and clustering statistic computation methods.

Additional context

This scenario occurs e.g. when reconstruction techniques are used.

Mesh-grid source data should demand less computational time as spherical harmonics can be precomputed and stored on the mesh grids.

[MikeSWang]

Consider more ambitious code porting to GPUs, depending on the memory requirements of concurrent 3D arrays.