Run SyncService.start() and stop() with a non-UI dispatcher

[jmartinesp]

Content

Run SyncService.start() and SyncService.stop() using a background dispatcher.

Motivation and context

The Rust code doesn't seem to handle coroutine cancellation in a nice way, so sometimes when the sync service too a bit longer than expected to run and several syncs tried to start at the same time a deadlock happened which blocked the main thread in Android.

Tests

To make testing easier, since I wasn't able to reproduce this issue on my test devices I built this branch of the SDK to make deadlocks more probable.

Then I opened the app and kept backgrounding it, then opening it back non-stop in short amounts of time: without this patch, I'd have an ANR at 5-6s max. With the patch I couldn't trigger it.

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

[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.26%. Comparing base (63dbf93) to head (dccb73c).
Report is 19 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4133   +/-   ##
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  Coverage    83.26%   83.26%           
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  Files         1885     1885           
  Lines        49127    49127           
  Branches      5774     5774           
========================================
  Hits         40907    40907           
  Misses        6144     6144           
  Partials      2076     2076           

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