Test if xugrid's and iMOD Python's Regridder behave similar enough

[JoerivanEngelen]

It would be good to test iMOD Python's regridder and xugrid's behave similar enough.
If there are any noticeable differences these should be documented.

[Huite]

The most important thing is that the xugrid one is missing the Voxelizer and LayerRegridder, essentially.

This requires top and bottom data, or bounds on a z coordinate. I've implemented the logic for computing the weights: https://github.com/Deltares/xugrid/blob/fc0bdcb0eaeff62887f1e62fadd61957629dff61/xugrid/regrid/overlap_1d.py#L158

But it's not exposed yet here (class exists: https://github.com/Deltares/xugrid/blob/fc0bdcb0eaeff62887f1e62fadd61957629dff61/xugrid/regrid/structured.py#L736)