Swap `curry` and `uncurry` to match math and Haskell

Per https://coq.zulipchat.com/#narrow/stream/237977-Coq-users/topic/prod_curry.2Funcurry.20seem.20named.20backward, the naming of prod_{curry,uncurry} is backwards in Coq and std++. I'm happy to send a MR, not today but next week.