Lots of code was using 32-byte nonces for xchacha20 symmetric
encryption, but this just means 8 extra bytes per packet wasted as
chacha is only using the first 24 bytes of that nonce anyway.
Changing this resulted in a lot of dead/dying code breaking, so this
commit also removes a lot of that (and comments a couple places with
TODO instead)
Also nounce -> nonce where it came up.
- RemoteRC supplants most of the functionality throughout the code of RouterContact
- Next step will be to sort out CI issues, then see if we can get rid of either LocalRC (and therefore RouterContact entirely)
- Get rid of CryptoManager.
- Get rid of Crypto.
- Move all the Crypto instance methods to llarp::crypto functions.
(None of them needed to be methods at all, so this is simple).
- Move sodium/ntru initialization into static initialization.
- Add llarp::csrng, which is an available llarp::CSRNG instance which is
a bit easier than needing to construct a `CSRNG rng{};` in various
places.
- Various related small simplifications/cleanups.