Xcode 12 and older incorrectly let us declare BIOSError.incorrectSize as @available(iOS 13), but Swift doesn't support @available for enum cases with associated values. Xcode 13 now properly enforces this restriction, so we instead mark the enum itself as @available(iOS 13).
DSi BIOS files can have various hashes, so rather than compare them against an expected hash, we now compare them against unsupported hashes and throw an error if it matches one.
