feat(data/nat/basic): (∀ a : ℕ, m ∣ a ↔ n ∣ a) ↔ m = n (#7132)
... and the dual statement
`(∀ a : ℕ, a ∣ m ↔ a ∣ n) ↔ m = n`
Zulip discussion:
https://leanprover.zulipchat.com/#narrow/stream/113489-new-members/topic/semilattice.2C.20dvd.2C.20associated
Co-authored-by: tb65536 <tb65536@users.noreply.github.com>
