upd: change event bus

- Make `.subscribeOnce` return listener id
- Make `.cancel` and `.isCanceled` methods in `MscEvent` implemented

include/engine/core/engine_bus.hpp

@@ -18,10 +18,19 @@ public:
     virtual std::string getName() const = 0;
 
     /// @brief Is current event is canceled
-    virtual bool isCanceled() const = 0;
+    bool isCanceled() const
+    {
+        return canceled;
+    }
 
     /// @brief Cancel current event
-    virtual void cancel() = 0;
+    void cancel()
+    {
+        canceled = true;
+    }
+
+private:
+    bool canceled = false;
 };
 
 /// @brief Engine event bus
@@ -47,7 +56,7 @@ public:
     /// @brief Subscribe to specified event and execute once on publish
     /// @param name event name
     /// @param listener event handler
-    void subscribeOnce(const std::string &name, Listener listener);
+    SubscriptionId subscribeOnce(const std::string &name, Listener listener);
 
     /// @brief Unsubscribe listener by its own id
     /// @param id subscription id