Broadcast.from(input[, options])

• input <AsyncIterable> | <Iterable> | <BroadcastChannel>
• options <Object> 与 broadcast() 相同。
• 返回：<BroadcastChannel> | <Object> 一个 broadcastProtocol 输入会直接返回它的 <BroadcastChannel>。其他输入会返回 { writer, broadcast }。

从现有来源创建一个 <BroadcastChannel>。来源会被自动使用，并推送给所有订阅者。

🌐 Create a <BroadcastChannel> from an existing source. The source is consumed automatically and pushed to all subscribers.