fix(client): encode the negotiated hash algorithm for RSA certificates

[inureyes]

Method::FutureCertificate carries a hash_alg, but both the probe request and the signed request encoded cert.algorithm().to_certificate_type(), which always yields ssh-rsa-cert-v01@openssh.com for an RSA certificate. A server that rejects SHA-1 signatures therefore refuses RSA user certificates even when the client selected SHA-256 or SHA-512.

client_make_to_sign now takes the certificate hash algorithm and applies it with with_hash_alg in both places, so the wire carries rsa-sha2-512-cert-v01@openssh.com or rsa-sha2-256-cert-v01@openssh.com when one is selected. Non-RSA certificates encode identically to before, and the self-signed OpenSshCertificate path passes None, so its behavior is unchanged.

A new test drives all three hash selections through both the probe and the signed request. Removing either with_hash_alg call makes it fail with ssh-rsa-cert-v01@openssh.com.

compression::tests::partial_flush_packets_round_trip fails on main at d3ae702 as well, and #757 looks like the fix. Everything else passes.

[Eugeny]

Thank you! @all-contributors add @inureyes for code

[allcontributors]

@Eugeny

@inureyes already contributed before to code