Stateless transport — caller supplies the nonce on every call.
Nonce uniqueness and replay detection are the caller’s responsibility.
Obtain via StrobeNkTransport::into_stateless().
Stateful transport — automatically increments nonces on each send/recv.
Obtain via StrobeNkHybridInitiator::finish() / StrobeNkHybridResponder::respond()
or the PQC equivalents.