feat: #944 - added a category picker page to the temporary product button

[monsieurtanuki]

What

• added a category picker page to the temporary product button

New files

• category_cache.dart: Cache where we download and store category data.
• category_picker_page.dart: Category picker page.
• product_refresher.dart: Refreshes a product on the BE then on the local database.

Impacted files

• new_product_page.dart: now the temporary button opens the category picker page.
• nutrition_page_loaded.dart: refactored using new class ProductRefresher.

Several points pending

1. manage the roots
2. manage the multi-category (e.g. green tea being considered in French as "thé" and "tisane")
3. make the "save to BE" work

Screenshot

Fixes bug(s)

• Implement a path to Category picker #877

Part of

• Road to Scores (tracker) #379

(please be as granular as possible)

[teolemon]

Are the different icons voluntary @monsieurtanuki , compared to the initial implem for search refinement ?

[monsieurtanuki]

As far as I know the implementation you're referring to 1. is still a draft 2. is on the search page ("let's filter all results even more by categories") and not on the product page ("let me set a more appropriate category for this product").
My choice of icons (radio buttons instead of check boxes) matches the need I understood: select one category for a product.
Regarding arrows, sure I can replace up-left and down-right arrows with left and right arrows.

[teolemon]

• You're right, it's 2 different uses of the same codes, with some variations
• Potentially, we'll have several categories, which checkbox carry slightly better.
• The division lines are helpful to convey hierarchy and the ability to deep dive (like in a File Explorer)
• The tags on top (with the already selected cats), and the ability to search within the full tree are useful for power users and people like @stephanegigandet who don't like delving progressively within 12 levels of hierarchy (I'm not sure if this one was already implemented)

[monsieurtanuki]

1. I understand the use-case of "category search" by string for power-users, but it's not going to be implemented in this PR - and I don't know if on the BE there's a query for that.
2. I don't know people that can understand browsing the same hierarchy in order to set several values: my assumption is that human beings can perform that one category at a time (hence the radio buttons). In the worst case scenario of several categories I guess we can use several category buttons - I have to look again at products with several categories (which is the minority I presume)
3. My understanding of the needs was to browse a hierarchy to fix the pre-defined category - e.g. maybe 2 steps deeper, maybe a sibling, maybe a cousin. I was thinking about a Unix ls / DOS dir command.
4. If you want I can add division lines, and print the full path in the .. line.

[teolemon]

@monsieurtanuki I guess since it's dev mode, and unless @M123-dev has some feedback, that's good with me (with the possibility to fix later)

[monsieurtanuki]

Thank you @teolemon for your review: of course UI and features can be fixed later.