Current usage of seeding rand in kmeans is not portable

[michaelkirk]

rand::StdRng is not portable, meaning (for example) that StdRng::from_seed(42).next_u32() will not necessarily give you the same output across machine/os/compiler configurations.

Our impetus for adding a seed configuration was to have repeatable CI. It's certainly more (mostly) repeatable, but might give different behavior across OS versions and on CI arch/os vs developer arch/os.

An alternative would be to use something portable like https://docs.rs/rand_chacha/latest/rand_chacha/

To be clear, I personally think this is low priority given our usage of rand, but I wanted to write it down before I forgot.