[chat example] How to simulate slow connection?

I want to observe in what scenario `closeSlow` is called, How to simulate slow connection mentioned in [websocket/internal/examples/chat/chat.go](https://github.com/coder/websocket/blob/v1.8.14/internal/examples/chat/chat.go#L120-L127)?:
```
s := &subscriber{
msgs: make(chan []byte, cs.subscriberMessageBuffer),
closeSlow: func() {
mu.Lock()
defer mu.Unlock()
closed = true
if c != nil {
c.Close(websocket.StatusPolicyViolation, "connection too slow to keep up with messages")
}
},
}
```

Start with internal/examples/chat/chat.go around lines 120-127 and trace the closeSlow callback through the chat example's subscriber behavior. Run the chat example while examining how messages reach the subscriber, then document a reproducible way to trigger the slow-connection condition and what result to expect.

Written by the indexing model from the issue text.