Add metadata about local Product, for better refresh flexibility

[monsieurtanuki]

Problem

We store products locally with only one metadata: the timestamp of the latest insertion/update in the local database (last_update).
If we want to do smart database refreshes (e.g. new language), that may not be enough.
"Smart" refreshes mean something more refined than "refresh all the products in one shot".

Proposed solution

The first example that comes to mind is the language. When we download a product, we call the API with a language parameter.
We could store locally the queried language as a metadata, at the same time as we store the product.
With that metadata, we could run queries like "give the local products in history that are not in Italian (new language), most recent first"

Of course, other metadata could be added.
Possibly, additional OFF metadata extracted from the product (like the OFF "last update"). For queries like "give me the local products whose server refresh is more than 2 months old".
Not sure if the country would be as relevant as the language.

Part of

• We need to sort out the refresh scenario. #4941

[monsieurtanuki]

My first tests are very interesting.
It looks like we'd be able to just frequently say "btw just refresh the most recent products that are not in the current language, and keep doing so".

[monsieurtanuki]

Possible improvement: a "last access" metadata, cf. @LuanRoger in #4717 (comment).
To be considered carefully: that would mean "writing" each time we "read" a product, and for the moment we write only when we download a product.

[monsieurtanuki]

Now that #4951 is merged, we have all we need to automatically refresh the products when the app language changes.
Smoothly.
The first step will be: "refresh 10 products that are not in the right language, and do it again".
Then some fine tunings, about which products are more interesting and should be refreshed first.

[monsieurtanuki]

@teolemon I'm sure you'll love that. I don't know if I'll be able to PR today but by the time I switched from the preferences (language: French -> Italian) to the history list, the products were translated!

French	Italian

[monsieurtanuki]

I've just lost all today's code because of merge conflicts with the important matter of #4938's test tube being empty or filled...

[monsieurtanuki]

With #4951 and #4969 now merged, we have 2 new metadata:

• the language of the server query when the product was downloaded
• the timestamp of the latest local access to the product (e.g. open product page or open product list page)

With those metadata it's very easy to solve the "app language change" problem:

• are there products that were not downloaded in the same language as the app?
• if so, let's download the products in the new language, for the most interesting products first (e.g. ordered by descending timestamp)

For the nutriscore refresh, the problem is a bit different:

• how do we know the nutriscore hasn't been potentially refreshed yet, in general or for a product? Like, if the product server last_update timestamp is prior a date, like April 1st 2024?
• how could we track which products we still have to refresh? A trick would be to empty the download-language metadata, which would trigger the database refresh on grounds of empty=wrong language.

[monsieurtanuki]

This week-end I'll PR the automatic translation system at each app language change.