Heartbeat: implement in both live-reload servers

[developit]

This updates #6904 to apply the heartbeat to both version of the live-reload server.

• Docs
• Tests

Testing Strategy:

Run a remix app in dev mode and load it via a Cloudflare tunnel:

npm run dev & cloudflared tunnel --url http://localhost:57763

Now open the tunnel URL and wait 100 seconds. The socket connection will be closed and the page will reload.

[changeset-bot]

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Latest commit: f160ce9

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[github-actions]

🤖 Hello there,

We just published version 1.19.1-pre.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version 1.19.1 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!