fix: 4564 - product immediately visible even if not on the server yet

[monsieurtanuki]

What

• For the record in our local database we only store full product data from the server. And we also store somewhere else pending changes to be applied on top. With this mechanism we can display fresh data locally before it's uploaded.
• The fix here was mainly on ProductModel.
• The idea was to say: if you don't find the product in the database, it's perhaps because it's not been sent to the server yet.
• The issue was about: it's not in the database and it's not on the server (which happens for products created locally before the upload), with the "unable to fetch information from the server" message.
• Instead we add an additional case: not in the database but with pending changes.

Screenshot

How to reproduce:

1. connected to internet
2. I select a barcode that does not exist (here, a fake book barcode)
3. it's unknown on the server: the app suggests me to create the product
4. I disconnect from internet
5. I add a detail (product name), and save the product.
6. I go to my "history"
7. I see the product I created (that's basically what the issue was about) though it is not on the server
8. I see a "PENDING..." banner that implies that pending changes have not been completely processed yet

Fixes bug(s)

• Fixes: An issue with background tasks? #4564

Impacted files

• fetched_product.dart: moved code from ProductRefresher
• product_cards_helper.dart: unrelated bug fix
• product_dialog_helper.dart: special case when the product was created locally but not uploaded/refreshed yet
• product_field_editor.dart: unrelated bug fix
• product_list_item_simple.dart: moved code to model
• product_model.dart: special case when the product was created locally but not uploaded/refreshed yet
• product_refresher.dart: moved code to FetchedProduct; minor refactoring
• smooth_product_card_found.dart: added a banner for product with pending changes.
• up_to_date_product_provider.dart: minor refactoring

[monsieurtanuki]

For the record, this is how Evernote marks notes as "not sync'ed yet". The sync'ed notes don't have the green triangle:

[codecov-commenter]

Codecov Report

Merging #4584 (b45875a) into develop (05d0490) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##           develop    #4584   +/-   ##
========================================
  Coverage    10.03%   10.03%           
========================================
  Files          312      312           
  Lines        15642    15635    -7     
========================================
  Hits          1569     1569           
+ Misses       14073    14066    -7     

Files Changed	Coverage Δ
...cards/product_cards/smooth_product_card_found.dart	0.00% <0.00%> (ø)
...es/smooth_app/lib/data_models/fetched_product.dart	13.04% <0.00%> (-20.29%)	⬇️
...p/lib/data_models/up_to_date_product_provider.dart	0.00% <0.00%> (ø)
...s/smooth_app/lib/helpers/product_cards_helper.dart	0.00% <0.00%> (ø)
...ib/pages/product/common/product_dialog_helper.dart	0.00% <0.00%> (ø)
...pages/product/common/product_list_item_simple.dart	0.00% <0.00%> (ø)
...th_app/lib/pages/product/common/product_model.dart	0.00% <0.00%> (ø)
...pp/lib/pages/product/common/product_refresher.dart	0.00% <0.00%> (ø)
...th_app/lib/pages/product/product_field_editor.dart	0.00% <0.00%> (ø)

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[teolemon]

@g123k can you have a look at the PR ?

[M123-dev]

I think the idea is good to visualize pending changes, but let's hide it in the dev mode first to think about where we have to display it too

Product page?
Product edit page?
The images if they are uploaded?
...

[monsieurtanuki]

Thank you @M123-dev for your review!
I've just removed the "pending..." banner as it was not at all the core of the fix, but rather a trial ballon.
If one day the "pending" banner is to be implemented, it will be in another PR.

[M123-dev]

Looks right to me, thanks @monsieurtanuki

[monsieurtanuki]

Thank you @M123-dev for your review!