InfiniInt<T> small-storage optimization

[oscbyspro]

InfiniInt<T> stores an array at the moment. I've occasionally thought about storing an enum that contains an array or one element. After more deliberation, I believe a tagged pointer (#43) is a better optimization. The latter ensures that the inline model fits in a register and there are still ptr - 1 bits to work with.

[oscbyspro]

Also, the compact bit count eliminates an annoying edge case (#3) (#6).