1107 LiveActivities instant updates fixes

[BPerlakiH]

Fixes: #1107

Make sure we handle background tasks.
Use more frequent updates, without timers, that the background task can cancel.
Do a direct update of live activities in scheduled background mode.
Fix the remaining time calculations.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 53 lines in your changes missing coverage. Please review.

Project coverage is 23.73%. Comparing base (0ea8330) to head (609dfe2).

Files with missing lines	Patch %	Lines
App/App_iOS.swift	0.00%	24 Missing ⚠️
Model/Utilities/DownloadTime.swift	0.00%	17 Missing ⚠️
Views/LiveActivity/ActivityService.swift	0.00%	11 Missing ⚠️
Model/Downloads/BackgroundDownloads.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1146       +/-   ##
===========================================
- Coverage   99.49%   23.73%   -75.76%     
===========================================
  Files          14      136      +122     
  Lines         785     7098     +6313     
===========================================
+ Hits          781     1685      +904     
- Misses          4     5413     +5409     

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[kelson42]

@BPerlakiH Please make a new testflight once merged