Responder's identity key pair.
Responder's signed pre-key private key (hex).
OptionaloneResponder's one-time pre-key private key (hex, optional).
Responder's PQ pre-key secret key (hex).
Initiator's identity public key (hex).
Initiator's ephemeral public key (hex).
ML-KEM-768 ciphertext from initiator (hex).
Parameters for responding to a PQXDH session (receiver side).