Simplify syncing the room list when receiving a push

[jmartinesp]

Content

We were previously creating a timeline for every room that received a push notification and waiting until the event was resolved for it before stopping the sync. Creating this timeline could be causing the unexpected UTD increase we've seen lately since the UTD hook now applies to any timeline, so we'll just give the sync a few seconds to run in background instead.

Motivation and context

Try to avoid UTDs and false marked-as-unread rooms.

Tests

With the app on background:

1. Receive a push.
2. Check the opportunistic room list sync starts (you can search for 'opportunistic' in the logs).
3. Check after ~10s the sync is stopped.

Tested devices

• Physical
• Emulator
• OS version(s): 14

Checklist

• Changes have been tested on an Android device or Android emulator with API 24
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly define what will change for the user
• Pull request includes screenshots or videos if containing UI changes
• You've made a self review of your PR

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.31%. Comparing base (7c79f8b) to head (6c0287a).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4915   +/-   ##
========================================
  Coverage    80.30%   80.31%           
========================================
  Files         2156     2156           
  Lines        57373    57360   -13     
  Branches      7225     7220    -5     
========================================
- Hits         46074    46066    -8     
+ Misses        8851     8850    -1     
+ Partials      2448     2444    -4     

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