seed not only `random` module but also `numpy`

[kjappelbaum]

https://github.com/lamalab-org/xtal2txt/blob/bf56bd86850a89870052cf2bbff27c3929732722/src/xtal2txt/core.py#L162

not clear to me what pymatgen is using

[n0w0f]

beleived to be implemented now #46 .

• [ ] check for other places where seeding is required