surface kpoint

[gitlzzz]

Do we have a function to check which direction is normal to the surface, although it is usually along z, we need to make it more robust.

https://github.com/pol-sb/MatDBForge/blob/5dcc5be7c237ae4d1e4c5dfa6ec1c66e3b68924d/src/MatDBForge/workflows/aiida_utils.py#L1183C1-L1183C23

[pol-sb]

Hey @gitlzzz,
I've prepared an approach that uses the spread of atomic positions in fractional coordinates: Assuming you have a slab, if you apply pbc, you should find that the axis with the highest distance between atoms is normally the one with the vacuum.

I tested this for usual slabs and it works.

[pol-sb]

Check #83