Parameters for initiating a PQXDH session (sender side).
Initiator's identity key pair.
Responder's identity public key (hex).
Responder's signed pre-key public key (hex).
Optional
Responder's one-time pre-key public key (hex, optional).
Responder's PQ pre-key public key (hex).
Parameters for initiating a PQXDH session (sender side).