Auth: CredSSP support

[irvingoujAtDevolution]

Gap

CredSSP is not supported. Some locked-down environments mandate it (and it enables credential delegation / second-hop). We currently support Negotiate/Kerberos/NTLM/Basic.

Current state

• Auth methods in crates/ironposh-client-core/src/connector/auth_sequence.rs / authenticator.rs (via sspi). No CredSSP path.

Required

• Add a CredSSP auth method (the sspi crate provides a CredSSP implementation — wire it into the auth sequence).
• WinRM message encryption with CredSSP uses its own MIME boundary and 16 KB chunking — implement the CredSSP wrap/unwrap path (distinct from SPNEGO sealing) in connector/encryption.rs.
• Expose --auth-method credssp in the tokio client.

Acceptance

• e2e: connect + run a command over HTTP with CredSSP (sealed) and over HTTPS, mirroring the existing transport/auth matrix cells.

References

• pypsrp encryption.py (CredSSP 16 KB chunking) + wsman.py credssp path.
• sspi crate CredSSP.