Draft: Attempt at cleaning up nearly all (macOS) warnings

Apple’s compiler (clang) really doesn’t like casts between non-pointer sized integers and pointers, and this currently happens all over the codebase even though almost all of it is actually harmless in practice. This change introduces a new spword/upword type to Types.h specifically for the cases where we’re storing integer-like values into pointers (going in both directions).

The changes were tested locally with Xcode 15.4 on my Mac Studio, and I verified that old save games I had still load ok. I also built the change locally on my Linux machine and verified the game at least comes up, although I don’t have any existing saved games.

I have a follow-on change (also a WIP) that just switches the entirety of the codebase to using stdint.h types in place of the custom types from Types.h, if anyone is interested in that.