Draft: Port to Hedgehog

Hedgehog's default shrinking behavior is considerably better than that of QuickCheck. It was easier to just move to Hedgehog than fix this.

For what it's worth, the documentation at shrink1 was much improved at some point, and nowadays getting good shrinks (probably better than hedgehog) is usually a matter of adding 3-4 lines shrink x = baseCase x ++ genericShrink x where baseCase x = someImmediateSubtermOf x

Hedgehog is cool. I still prefer quickcheck, my opinion oviously isn't a dealbreaker. I do hope the rewrite didn't introduce bugs or changed behavior, of course. Hard to tell with CI being broken. I did do a quick review of the code and nothing jumped out at me.

Any chance CI could be fixed first, though?