Requiring Show1 for Show, Eq1 for Eq, etc., is inconvenient

[robrix]

Once upon a time, fastsum had separate Apply and Apply1 typeclasses s.t. we could use Apply for Show and Apply1 for Functor. We eventually got rid of the former because compile times were already far too high, and instead used Show1 to provide our Show instance.

However, while it’s easy to derive Show instances, Show1 is not derivable, so you have to do a bunch of extra work just to show your Sums.