Symmetry operations in Cartesian and crystal coordinates

[HaritzGarai]

We should implement a subroutine in symmetries.f90 to transform symmetry operations from Cartesian to crystal coordinates and vice versa (s_cryst_to_cart with +/-1 as for the atomic positions). In the meeting on 01/12/2023, we agreed that this subroutine should use matmul to preform the matrix multiplications to make the code more readable.

[HaritzGarai]

Instead of implementing a subroutine to transform symmetries from Cartesian coordinates to crystal coordinates and vice versa, I think we could create both variables s_cryst and s_cart and store them in memory. Since symmetries are used in many places throughout intw, and in terms of memory this won't have a big impact, I think that this is a better solution.