Update the chat example to publish messages on the websocket connection

I think the chat example would be a lot more valuable if the messages were published via the websocket connection instead of as separate HTTP request. I'm trying to migrate from gorilla/websockets but having a hard time figuring out how to both read from and write to a client from different threads. If not publishing the messages themselves, maybe a "typing" indicator when a user is typing in the input? Anything that demonstrates concurrent full duplex communication over websockets really.

先定位并运行聊天示例，然后检查它当前如何通过 HTTP 发送消息。该 issue 提议将消息发布移到 WebSocket 连接上，或添加输入指示器，以演示并发的 full-duplex 通信。在定义 done 之前，先确认接受哪种行为。

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