Hide remaining time in UI when paused

[JanuarySnow]

closes #510

Hides the UI element text for time remaining when throughput is effectively zero (paused)

Thought it was better hidden rather than saying "0 seconds remaining" which might be a bit misleading.

Normal:

Paused:

[Sewer56]

CC @captainsandypants (<= UX/design).

---

The code part is fine, because paused jobs return AdditiveIdentity as their throughput (i.e. 0).

[Sewer56]

Code is OK, however please don't merge without input from design.

[JanuarySnow]

Updated test code to check for the empty string instead of the numerical value when downloads are paused

[codecov]

Codecov Report

Merging #571 (f95ee7e) into main (b34be79) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #571      +/-   ##
==========================================
- Coverage   68.14%   68.14%   -0.01%     
==========================================
  Files         602      602              
  Lines       16204    16213       +9     
  Branches     1103     1104       +1     
==========================================
+ Hits        11042    11048       +6     
  Misses       4876     4876              
- Partials      286      289       +3     

Flag	Coverage Δ
Linux	67.42% <100.00%> (+0.05%)	⬆️
Windows	67.24% <100.00%> (-0.07%)	⬇️
clean_environment_tests	68.14% <100.00%> (+<0.01%)	⬆️

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

Files Changed	Coverage Δ
...ightContent/Downloads/InProgressCommonViewModel.cs	98.29% <100.00%> (ø)
....UI/RightContent/Downloads/InProgressView.axaml.cs	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

[Al12rs]

Thanks for the contribution!