Use existing JS Websocket

Hello, I am wondering, with this library, is it possible to use an existing WebSocket that was created in JS land, something like

```go

exportConnect := js.FuncOf(func(this js.Value, args []js.Value) any {
// ...

socket := args[0]
conn, _, err := websocket.From(ctx, socket)
netconn := websocket.NetConn(ctx, conn, websocket.MessageBinary)

// ...
})
js.Global().Set("go__connect", exportConnect)
```

Start by reviewing the websocket.From and websocket.NetConn entry points shown in the issue, along with the library's WebSocket and JavaScript interop documentation. Determine whether an existing JavaScript WebSocket can be supported and define the expected behavior and tests before implementation; done means the capability is documented and verified with a working example or test.

由索引模型根据 Issue 内容生成。