Updated Zenoh subscriber and queryable declarations to undeclare enti…

…ties when references are dropped. (#237)

zenoh-plugin-mqtt/src/lib.rs

@@ -184,6 +184,7 @@ async fn run(
     let _admin_queryable = zsession
         .declare_queryable(admin_keyexpr_expr)
         .callback(move |query| treat_admin_query(query, &admin_keyexpr_prefix, &config2))
+        .undeclare_on_drop(true)
         .await
         .expect("Failed to create AdminSpace queryable");
 

zenoh-plugin-mqtt/src/mqtt_session_state.rs

@@ -83,6 +83,7 @@ impl MqttSessionState {
                         tracing::warn!("{}", e);
                     }
                 })
+                .undeclare_on_drop(true)
                 .allowed_origin(sub_origin)
                 .await?;
             subs.insert(topic.into(), sub);