random cleanup of cpu stuff and tests
sbc and lots more test

holy shit i'm so tired of the V_FLAG. For ADC the overflow rules are so
easy. SBC is so confusing. I've read a few implementations and a few
explanations. I still haven't found rules for SBC and the V_FLAG that I
truly understand. And Im'n not willing to just copy somebody's code.
Idk. SBC. I know I've done it before. (Although I don't know if I've
ever written this many tests.) So. It's still on the to-do list. I can
still continue even if I don't know one single thing. That's something I
need to remember. Just because I don't quite have SBC doens't mean I
shouldn't do STX. At least if I did STX I'd figure out the memrory
write. And I sitll don't have a PPU objecgt, which is terrifying. The
APU isn't even on the schedule for this VERSION. Which is funy, that I'd
think of this personal project in terms of V1. Idk, I've never written
something like this before. Thanks github.