Explicitly pausing or stopping the track should save the current track progress

[SyntaxBlitz]

Right now, track progress is saved every 3 seconds when the app is backgrounded. This means stopping the lesson and then returning to it may result in a short progress loss. It's not a huge deal, and it can actually be kind of nice to get a few extra seconds of context when you come back to the track, but it would be better to implement this context deliberately instead of relying on a 'luck of the draw' based on when the progress was last saved.

An explicit stop or pause request from the notification should save the current progress immediately.