public WindowAsyncObservable(IAsyncSubject <TSource> subject, RefCountAsyncDisposable disposable)
 {
     _subject    = subject;
     _disposable = disposable;
 }
 public GroupedAsyncObservable(TKey key, IAsyncSubject <TElement> subject, RefCountAsyncDisposable disposable)
 {
     Key         = key;
     _subject    = subject;
     _disposable = disposable;
 }