SSH transport does not support newer encryption formats

[hiddeco]

During the consumption of this library we ran into a limitation of the NewPublicKeys helper present in the SSH transport library, which does not seem to support newer encryption formats like PEM blocks with a password protected ED25519 key.

Mitigation of this issue, even as a consumer, is fairly easy by creating our own helper that makes use of ParsePrivateKey and ParsePrivateKeyWithPassphrase from crypto/ssh, but it would likely be better if the library itself would switch to using these functions.