refactor(app): Refactor the application for simplicity

[edabe]

Current behavior:
In the current implementation,index.ts connects to different sensors (pwr, fe, cad and hr) and handles events via onDetected and onData callbacks. Sensors constantly trigger detected and data events when connected and in range.

The app passes detected events to the HeartRateMode class via onDetectedHandler callback, which allows it to implement the logic that determines what to do when the sensor is detected or not.

In this case, if onDetectedHandler is not called within a set interval, HeartRateMode will clean itself up.

Improved approach:
Decouple the ANT+ connection logic from the index.ts file; there should be a new ANT connection class that implements this logic.

Modify the HeartRateMode behavior so that it only exposes a cleanup and onDataHandler methods.
Modify the ANT connection logic so that it leverages onDetected to monitor sensors and, after a set interval of inactivity, call cleanup from HeartRateMode.

Improve testing to cover the new refactoring.