refactor: background tasks with classes

[monsieurtanuki]

New files:

• abstract_background_task.dart: Abstract background task.
• background_task_details.dart: Background task that changes product details (data, but no image upload).
• background_task_image.dart: Background task about product image upload.

Impacted files:

• add_basic_details_page.dart: refactored the call to background task; minor refactoring
• background_task_helper.dart: moved most of the code to new classes AbstractBackgroundTask and offsprings.
• edit_ingredients_page.dart: refactored the call to background task
• nutrition_page_loaded.dart: refactored the call to background task
• picture_capture_helper.dart: refactored the call to background task
• simple_input_page.dart: refactored the call to background task
• simple_input_page_helpers.dart: added and implemented method getTask

What

• The goal is to refactor and make easier the use of background tasks. Currently implemented: image upload and product changes.

Part of

• Reload the product on upload/edit task success #2968

[codecov-commenter]

Codecov Report

Merging #2994 (d2d614c) into develop (d2f8077) will increase coverage by 0.01%.
The diff coverage is 0.60%.

@@            Coverage Diff             @@
##           develop   #2994      +/-   ##
==========================================
+ Coverage     6.50%   6.51%   +0.01%     
==========================================
  Files          241     244       +3     
  Lines        12031   12026       -5     
==========================================
+ Hits           783     784       +1     
+ Misses       11248   11242       -6     

Impacted Files	Coverage Δ
...h_app/lib/background/abstract_background_task.dart	0.00% <0.00%> (ø)
...ooth_app/lib/background/background_task_image.dart	0.00% <0.00%> (ø)
...smooth_app/lib/helpers/background_task_helper.dart	0.00% <0.00%> (ø)
...smooth_app/lib/helpers/picture_capture_helper.dart	0.00% <0.00%> (ø)
..._app/lib/pages/product/add_basic_details_page.dart	0.00% <0.00%> (ø)
...h_app/lib/pages/product/edit_ingredients_page.dart	0.00% <0.00%> (ø)
...h_app/lib/pages/product/nutrition_page_loaded.dart	0.00% <0.00%> (ø)
...mooth_app/lib/pages/product/simple_input_page.dart	0.00% <0.00%> (ø)
...p/lib/pages/product/simple_input_page_helpers.dart	0.00% <0.00%> (ø)
...th_app/lib/background/background_task_details.dart	1.61% <1.61%> (ø)

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[AshAman999]

Honestly, I am impressed, thanks a lot for the great refactoring
I just left a real few minor issues, Just come better comments suggestions

[AshAman999]

Thank you @monsieurtanuki for this PR
Totally worth something to learn from

[monsieurtanuki]

Thank you @AshAman999 for your enthusiastic review!
For the record I found your initial decision to "reject" my PR excessive, if I write in British understatement mode.
Please do reject my PRs when there's something dangerous for the app integrity or consistency, but not for a couple of typos in comments. Just "comment" or "approve", that won't prevent me from fixing whatever you pointed out, if relevant.
The good news is that you liked the rest of the code! ;)

[AshAman999]

For the record I found your initial decision to "reject" my PR excessive, if I write in British understatement mode.
Please do reject my PRs when there's something dangerous for the app integrity or consistency, but not for a couple of typos in comments. Just "comment" or "approve", that won't prevent me from fixing whatever you pointed out, if relevant.

I didn't give much thought when selecting the review dropdown, honestly, to me all of them looked the same
I will be better responsible with the tags, sorry for the inconvenience though