Only connect to heartbeat if needed

[freddyaboulton]

Description

Closes: #8022

Rather than always connecting to the heartbeat route, we should do so only when gr.State variables are used (to clean up state) or when the unload event is set. Users may still run into the browser limit, however.

EDIT: I originally wanted to raise an error or message when the page locked up due to the connection limit. But the browser will block all requests after the limit is reached so we won't be able to fetch the config and progressively load the app.

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Only connect to heartbeat if needed

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[abidlabs]

Will this be compatible with gr.render() -- now that we can dynamically create components, a developer might include a workflow that dynamically creates gr.State() components?

The only other idea I can think of is to use long polling instead of a persistent SSE connection for the heartbeat

[freddyaboulton]

One of the reasons we did not use long-polling was that browsers can slow down timers so it could not be reliable. We're sending an updated config when the components are added in gr.render, I think we can recalculate the connect_heartbeat flag on every re-render.

[pngwn]

Looks great! Thanks @freddyaboulton!

Note: this should working fine with the render decorator because we refresh the config, as freddy mentioned.

[aliabid94]

LGTM!

[freddyaboulton]

Thanks for the reviews all!