Move downloads out of Temp and clean up after cancel and complete

[Al12rs]

• fixes Closing App cancels all ongoing downloads #1663

Ongoing download files are now stored next to DataModel folder, in Downloads/Ongoing.
Each download task will have a separate folder (guid name), which simplifies cleanup on download cancellation and download completion.

The base folder for the Downloads is determined by a setting, but it can be overruled through an internal method for testing purposes (so that each test has a different download base folder).

[Al12rs]

Need to look into the test not passing on windows
EDIT: Test appears to be flakey

[Al12rs]

I will change the tests to use a Setting override, since it should actually be better for running tests concurrently

[Al12rs]

Used the setting override in the tests, tests pass locally and it doesn't seem like any files are left around after the test (the folder structure yes, but it is empty).

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 91.42857% with 6 lines in your changes missing coverage. Please review.

Project coverage is 40.22%. Comparing base (cdfcc2d) to head (5feae1f).
Report is 16 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1704      +/-   ##
==========================================
- Coverage   42.15%   40.22%   -1.93%     
==========================================
  Files         769      706      -63     
  Lines       26393    24873    -1520     
  Branches     1999     1885     -114     
==========================================
- Hits        11126    10006    -1120     
+ Misses      14895    14533     -362     
+ Partials      372      334      -38     

Flag	Coverage Δ
Windows	40.09% <88.57%> (?)
clean_environment_tests	40.20% <90.00%> (-1.95%)	⬇️
macOS	39.44% <88.57%> (-2.72%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...exusMods.Networking.Downloaders/DownloadService.cs	55.17% <100.00%> (+2.96%)	⬆️
...rking/NexusMods.Networking.Downloaders/Services.cs	100.00% <100.00%> (+9.09%)	⬆️
...Mods.Networking.Downloaders/Tasks/ADownloadTask.cs	82.71% <100.00%> (+1.50%)	⬆️
...ds.Networking.HttpDownloader/DTOs/DownloadState.cs	100.00% <100.00%> (ø)
...ns/DownloadStatus/DownloadStatusDesignViewModel.cs	76.78% <ø> (+1.34%)	⬆️
...etworking.HttpDownloader/AdvancedHttpDownloader.cs	70.69% <80.00%> (ø)
...ttpDownloader.Tests/AdvancedHttpDownloaderTests.cs	0.00% <0.00%> (ø)
...xusMods.Networking.Downloaders/DownloadSettings.cs	84.61% <84.61%> (ø)

... and 65 files with indirect coverage changes