ssh-mldsa44-ed25519 support

[EvelyneSides]

With OpenSSH 10.6, the quantum resistant key type ssh-mldsa44-ed25519 has been stabilized.
I understand that age doesn't really want people to be using ssh identities, but I think it would be nice to implement support for them nonetheless to not discourage people from switching to quantum resistant keys ^^

[FiloSottile]

That’s simply not possible. SSH keys are signing keys, it was a hack to repurpose them for encryption, and ML-DSA does not lend itself to similar hacks.