fix: trig hold when entering menu to avoid flickering

main.c

@@ -1893,6 +1893,9 @@ void enter_menu_mode(void) {
   app.last_disp_sent[0] = '\0';
 
   save_dmm_state();
+  // Trigger Hold (T4) to make sure no new measurements
+  // interrupt our display while we're going through the menu
+  gpib_send(app.dmm_addr, HP3478A_TRIG_HOLD);
 
   app.current_mode = MODE_MENU;
   app.menu_pos = MENU_REL;