Notification might be skipped if app keeps working in the background

[danielgranhao]

There is no evidence this has happened in practice, but as @roeierez theorized here, it might be possible for the notification plugins to skip notifications if the app runs simultaneously in the background.

The notification plugins wait for some events issued by the SDK. If the app is running in the background, 2 SDK instances will run in parallel, and it's possible only a single one will emit the event. Let's investigate if this is indeed a potential issue and if so, decide how to fix it.

[danielgranhao]

The issue described above is unlikely because a backgrounded app is quickly throttled or even stopped. Despite that, assuming the SDK instance from a background app can process some update and issue an event accordingly, the SDK instance from a notification handler will effectively miss it.

I'll shortly open a PR that prevents this.