fix: 4074 - added explicit isolate/ui settings

[monsieurtanuki]

What

• In some background tasks we manipulate pictures, which can be costly performance wise. That's why we recently switched to isolates, for some specific operations.
• For some reason the "isolate" part was not working anymore - or maybe it never worked on some specific cases.
• Looking back at the doc, the question was "how could it work before?".
• Anyway, now it works, and I even added an additional safety test, running the same method as non-isolate if relevant.
• For my tests it was useful to add a "refresh" button on top of the background task page (typically in order to run again tasks in error), and I think we should keep that button.

Screenshot

New refresh button on top of background task page:

Fixes bug(s)

• Fixes: Image are not sent (Isolate/Background related) #4074

Impacted files

• image_compute_container.dart: added explicit isolate/ui settings
• offline_tasks_page.dart: added a "refresh" button on the app bar

[codecov-commenter]

Codecov Report

Merging #4080 (9f22858) into develop (6c292c0) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #4080      +/-   ##
===========================================
- Coverage    10.93%   10.92%   -0.02%     
===========================================
  Files          271      271              
  Lines        13454    13470      +16     
===========================================
  Hits          1471     1471              
- Misses       11983    11999      +16     

Impacted Files	Coverage Δ
...mooth_app/lib/helpers/image_compute_container.dart	0.00% <0.00%> (ø)
...kages/smooth_app/lib/pages/offline_tasks_page.dart	1.81% <0.00%> (-0.19%)	⬇️

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[alexgarel]

The refresh button is a good idea :-)

[monsieurtanuki]

The refresh button is a good idea :-)

I had to fix the bug too, or else you would only get refreshed errors ;)
Btw the refresh is somehow automatic anyway, e.g. if you go to a product page.