Queued toasts

Show three persistent toasts with a visible limit of two. The third waits until a visible toast closes.

1. Create three toasts. Only Toast 1 and Toast 2 should appear.
2. Update the waiting toast. Each click applies two consecutive updates without showing it.
3. Dismiss the oldest visible toast. Toast 3 should appear with its latest update count.

To test cancellation, reset, create three toasts, and dismiss the waiting toast before closing the visible ones.