ML-KEM through Python cryptography

[galaxymaster2007]

As of v48.0.0, the cryptography library supports ML-KEM:

pyca/cryptography#14598
pyca/cryptography#14781

This means AsyncSSH can now support post-quantum key exchange without liboqs.

[ronf]

Thanks - I did some early investigation on this back in April (see my comments in pyca/cryptography#12824) before the OpenSSL support was added. The proposed API backed up by BoringSSL was able to interoperate with my liboqs calls. I haven't yet tried to get this working with OpenSSL, but that'll be the next step.

Unfortunately, it's unlikely PyCA will pick up support for SNTRUP, so you'll still need to keep the liboqs dependency if you want to use that for key exchange. It also means I can't just replace the existing liboqs wrapper. I'll need to split it so ML-KEM has a separate wrapper from SNTRUP.