Android and iOS oauth

Caveats: - All the dependencies are broken because PBC sucks and probably never tested them so they had to be patched. - @atproto/oauth-client-expo uses upstream react-native-mmkv on an incompatible version. Instead of patching every file in there to point to @bsky-app/react-native-mmkv I renamed our @bsky-app/react-native-mmkv. This may cause regrets when merging so keep it in mind. When they change to new arch it shouldn't be a problem anymore as that is the only reason we need a fork of react-native-mmkv.