1008 unexpected data message: When using htmx client

Hi,

I seem to be having issues using this library when using it htmx as the client, specifically version 2 of htmx. I am also testing this on Firefox (if browser may make a difference.
I tend to see either this error `Connection Closed: 1008 unexpected data message` or sometimes I see `Invalid RSV bits ...`.

I am not sure how to debug what is going on. But I noticed there was another issue where someone getting similar errors in issue #339.

I tried using another library, https://github.com/gobwas/ws, and it seems to work with this library :thinking:. See this commit here for an example where it works: https://gitlab.com/hmajid2301/banterbus/-/commit/a7501484832f51f430e83da1e39dacd01a0b6860.

See this commit here for a version with this library causing issues: https://gitlab.com/hmajid2301/banterbus/-/blob/9bcd9d73690df9cd3fdcddafc4498a1428497210/internal/transport/http.go

Please let me know if there is anything I can do to help :heart: .

## Reproduce

```bash
git clone https://gitlab.com/hmajid2301/banterbus.git
git checkout 9bcd9d73690df9cd3fdcddafc4498a1428497210
go run main.go

# Go to localhost:8080
```

- Try to submit the input `Create Room`
- Inspect network traffic
- Notice the error in the response
- Of the web socket request


## Version

```shell
cat go.mod
# ...
nhooyr.io/websocket v1.8.11

cat index.html
#
https://unpkg.com/htmx.org@2.0.0
https://unpkg.com/htmx-ext-ws@2.0.0/ws.js

firefox --version
Mozilla Firefox 128.0
```

Reproduce with the banterbus repository at commit 9bcd9d73690df9cd3fdcddafc4498a1428497210, run `go run main.go`, and submit “Create Room” from Firefox with htmx 2.0. Start by reading internal/transport/http.go and comparing it with the working gobwas/ws commit. Inspect the WebSocket network response to isolate the 1008 or RSV error; done means the cause is identified and the htmx reproduction works or has clear guidance.

Written by the indexing model from the issue text.