Improve FetchPushForegroundService's reliability

[jmartinesp]

Content

• Don't use DI, we can just create the notification channel. This should speed up the creation of the service and reduce the number of ForegroundServiceDidNotStartInTimeException received. Also use MainScope instead of the app's coroutine scope.
• Move the wakelock releasing mechanism to onDestroy so it's always used. Previously, this would only happen when stopService was called, which would only happen when stopSelf() is called, but not when the OS or the service manager stops the service.

Motivation and context

Fix the ForegroundServiceDidNotStartInTimeException we're still seeing in Sentry.

Tests

Just use notifications as usual.

Tested devices

• Physical
• Emulator
• OS version(s): 15

Checklist

• This PR was made with the help of AI:
  • Yes. I asked Claude what could be causing the issues, which confirmed a suspicion of mine and also added a possible cause I hadn't identified.
  • No.
• 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 defines 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

[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

❌ Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.21%. Comparing base (4a4b3e0) to head (58a1b05).

Files with missing lines	Patch %	Lines
...aries/push/impl/push/FetchPushForegroundService.kt	0.00%	19 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6757      +/-   ##
===========================================
- Coverage    81.22%   81.21%   -0.01%     
===========================================
  Files         2633     2633              
  Lines        73426    73433       +7     
  Branches      9490     9491       +1     
===========================================
  Hits         59638    59638              
- Misses       10300    10307       +7     
  Partials      3488     3488              

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