mathlib

69066273 - refactor(algebra/squarefree): split out `nat` part to new file `data/nat/squarefree` (#14577)

refactor(algebra/squarefree): split out `nat` part to new file `data/nat/squarefree` (#14577) As discussed in this Zulip [thread](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/squarefree.2C.20is_prime_pow.2C.20and.20factorization)