introduce new numpy random_state, especially in store, for reproducibility

[bkmi]

For reproducibility there is the option to split the seed, we should use it.

https://numpy.org/doc/stable/reference/random/index.html?

https://github.com/undark-lab/swyft/blob/07a5bffb543b4afab050cfc63c897215ccb6b355/swyft/store/store.py#L94-L131

[bkmi]

This would be nice for the next release, for reproducibility when dealing with multiprocessing.

[cweniger]

This would be still useful, keep it for v0.4 as optional enhancement.