Add a heuristic for case-lambda type simplification.
Add a heuristic for case-lambda type simplification.

Makes simplification _much_ faster for types that have a single most
general case. That includes most numeric functions.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket