game-boy: Implement model and palette handling

I originally wanted to do it on mGBA side, but while it's more work, it's both cleaner and more robust to do it on the frontend. For example, now we can know if a game is GBC-only/GBC with GB compatibility/SGB-enhanced, whether it has special palettes on GBC or SGB, as well as whether it's GBA-enhanced or has special features on SGB2 - without launching the game.