Switching to rng.spawn() with numpy 1.25

[thuiop]

Whenever we switch to having numpy 1.25 as a requirement (not necessarily soon since it is currently the latest stable version), we should switch to rng.spawn() to divide the random number generator instead of handling the seedsequence like it is currently done. https://numpy.org/doc/stable/release/1.25.0-notes.html#ability-to-directly-spawn-random-number-generators