Added SumProfunctor instance for Costar (but needs adjunctions)

[duairc]

I expect that you're less likely to merge this one (because it adds a dependency on adjunctions), but for what it's worth, Costar actually can be made into a SumProfunctor, but it needs cozipL.

[tomjaguarpaw]

Can I ask why this is useful in practice?

[sjoerdvisscher]

Imho it is not very useful, since for left adjoints f, f a is isomorphic to (a, f()), so Costar f a b is isomorphic to (a, f ()) -> b, which is isomorphic to Star ((->) (f ())) a b.

It could still be useful if Adjunction is a much used class, but afaik it isn't.