small improvement

satrs-minisim/src/acs.rs

@@ -148,10 +148,7 @@ impl MagnetorquerModel {
     pub fn send_housekeeping_data(&mut self) {
         let mgt_reply = MgtReply::Hk(self.torque_dipole);
         self.reply_sender
-            .send(SimReply {
-                device: SimDevice::Mgt,
-                reply: serde_json::to_string(&mgt_reply).expect("failed to serialize MgtReply"),
-            })
+            .send(SimReply::new(SimDevice::Mgt, mgt_reply))
             .unwrap();
     }