[Feature Request]: Document the new extension API?

### Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

### What would your feature do ?

Hi,

I'm migrating to ts and use the published types which showed a deprecation:

But the [docs](https://docs.comfy.org/custom-nodes/js/javascript_overview#registering-an-extension) still mention the old way and I can't find how to use this new "hook" / provider concept

### Proposed workflow

Add documentation for `useExtensionService`

### Additional information

_No response_

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