Switching to rng.spawn() with numpy 1.25

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