Feature/android background audio source

[tonelli-m]

Description

Bind the audio source to a Foreground Service to keep it running when the app is in the background.

Changes

• Added an AudioSourceService class for Android that will take care of handling the audio thread as a foreground service
• A persistent notification will be shown in the notification center while the service is running
  • Notifications permission needs to be granted to show notifications for android 13 (tiramisu) and above. The service can still run if the user denies permission, only the notification will not show.
  • For Android 14 (Upside down cake) and above, the persistent notification can still manually be dismissed, it will not stick. However dismissing the notification doesn't stop the service either, it simply removes it from the drawer. More details

Linked issues

#49
#38

Remaining TODOs

• This is just a basic implementation of a foreground service, it may need to be tweaked to reduce even more the chances of the service being killed by the system. Further testing on a broader range of devices would be needed for this.
• ATM the service is start as soon as the measurements screen is open and is directly tied to the audio source. Later, we might want to keep both separate to only start the service when a recording has been explicitly started by the user. This will be the scope of another PR though as all the elements are not yet present for a more complex implementation.
• We may want to add some controls and additional information to the notification in the future like duration of the measurement, pause/resume/stop buttons, etc.

Checklist

• Code compiles correctly on all platforms
• All pre-existing tests are passing
• If needed, new tests have been added
• Extended the README / documentation if necessary
• Added code has been documented