Fixed: Duplicate resume/cancel buttons in download notification.

[MohitMaliFtechiz]

Fixes #4235

• When there is a single download running, and we pause the download from the notification then we push a custom notification and update the foreground service notification. So when we are pushing our custom notification it is performing on the IO thread, and when we are setting it on the foreground service, then instead of updating the same notification it creates a new notification and shows it, and in the meantime, our pushing the cancel notification finishes and push a second notification. Due to the same notification ID, it updates the same notification but its actions(resume/cancel) are added twice.
• We fixed it by synchronizing the process. Now, it first pushes the notification for paused download, and then if there is no other downloading going then it will set the current notification to foreground service.

Before Fix

BeforeFix.mp4

After Fix

AfterFix.mp4

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.50%. Comparing base (b025813) to head (765da6b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4239      +/-   ##
============================================
- Coverage     57.83%   57.50%   -0.34%     
+ Complexity     1597     1581      -16     
============================================
  Files           316      316              
  Lines         14063    14059       -4     
  Branches       1740     1740              
============================================
- Hits           8134     8085      -49     
- Misses         4731     4781      +50     
+ Partials       1198     1193       -5     

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