Expose-status-of-assist-as-a-sensor

[ujjol1234]

Summary

This PR introduces a Assist Sensor in the companion-app that shows whether Assist on the phone is listening.

Checklist

• [ ] New or updated tests have been added to cover the changes following the testing guidelines.
• [ ] The code follows the project's code style and best_practices.
• [ ] The changes have been thoroughly tested, and edge cases have been considered.
• [ ] Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

[home-assistant[bot]]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks :+1:

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[jpelgrom]

Did you test the app with this sensor and is it updating the state as expected (idle > listening > speaking > idle)? Did you also test with keyboard input / interrupting the microphone manually / dismissing the sheet while recording/playing?

This will also need a documentation PR to be accepted.

[ujjol1234]

@dshokouhi @TimoPtr thank you for the feedback. I have implemented the changes.