public void OnSubjectRemove(ISubject <DeathEvent> subject)
    {
        DeathSubjects.Remove(subject);

        ObserverSubjectBridge bridge = ObserverSubjectBridge.Instance;

        foreach (IObserver <DeathEvent> observer in _secondaryDeathObservers)
        {
            bridge.RemoveObserverFrom(observer, subject);
        }
    }
    public void OnSubjectAdd(ISubject <DeathEvent> subject)
    {
        DeathSubjects.Add(subject);

        ObserverSubjectBridge bridge = ObserverSubjectBridge.Instance;

        foreach (IObserver <DeathEvent> observer in _secondaryDeathObservers)
        {
            bridge.RegisterObserverTo(observer, subject);
        }
    }