Guard vendored CRI message handling against null teardown frames

[Copilot]

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Description

The vendored Chrome DevTools Protocol client could throw an uncaught TypeError during browser/socket teardown when a WebSocket frame parsed to null. This updates the message handler to ignore null/non-object teardown frames so the axe transport fail-closed path rejects in-flight commands without crashing the test module.

• Problem

  • dropped-socket teardown frames could reach _handleMessage() as null
  • the existing message.id dereference escaped from the WebSocket event handler as an uncaught error

• Change

  • add a narrow guard at the top of src/core/cri/deno-cri/chrome.js::_handleMessage
  • leave command-response (message.id) and event (message.method) handling unchanged for well-formed protocol messages

• Effect

  • connection-teardown noise is ignored
  • normal CDP responses and events keep the existing behavior

```js
_handleMessage(message) {
  if (!message || typeof message !== "object") {
    return;
  }

  if (message.id) {
    ...
```

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

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[cderv]

I am merging because it fixes what it should (https://github.com/quarto-dev/quarto-cli/actions/runs/35338223335/job/105577961196) and the test above are failing on main - looking at that in another PR.