LP: mixnet reg fixes (#6356)

* removed x25519 key used within LP mixnet registration

* use Vec<u8> rather than BytesMut for LpAction::DeliverData

* introduced an explicit kind prefix for raw data sent and received within LP

* review nits

integration-tests/src/lp_registration.rs

@@ -529,6 +529,7 @@ mod tests {
 
         #[tokio::test]
         async fn test_basic_lp_exit_registration() -> anyhow::Result<()> {
+            // nym_test_utils::helpers::setup_test_logger();
             // initialise random, but deterministic, keys, addresses, etc. for the parties
             let mut client_rng = u64_seeded_rng(0);
             let mut entry_rng = u64_seeded_rng(1);
@@ -652,7 +653,6 @@ mod tests {
                     exit.base.peer.ed25519().public_key(),
                     &client_data.ticket_provider,
                     TicketType::V1WireguardExit,
-                    client_data.base.socket_addr.ip(),
                 )
                 .timeboxed()
                 .await??;