fix: 4957 - SVG icons are now correctly refreshed when their URL change

[monsieurtanuki]

What

• The SVG icons were not refreshed when the underlying URL changed (e.g. after a product category change).
• The fix is to use the SVG icon widget with a URL-related key. That will trigger the refresh of the StatefulWidget when relevant.

Fixes bug(s)

• Fixes: Product page partially updated #4957

Impacted files

• asset_cache_helper.dart: added a relevant key
• svg_cache.dart: used the helper key so that flutter does refresh the widget for different URLs
• svg_safe_network.dart: used a key; unrelated error message improvement

[teolemon]

This will ensure the Nutri-Score transition, am I right ?

[monsieurtanuki]

This will ensure the Nutri-Score transition, am I right ?

Only in some very very rare cases.

For the new Nutri-Score transition rather have a look at #5100 - which is only a suggestion. I haven't seen anything new about the Nutri-Score transition in #4545.

For that specific PR it's about the way flutter works: for some kinds of widgets (StatefulWidgets) we sometimes need to add a relevant key.
If I see a nutriscore icon widget on a product page, then edit the product and then go back to the product page, the nutriscore icon widget will not be refreshed. That widget is loaded asynchronously and uses a State which somehow hides its data - including the URL. flutter will say "AFAIK this widget and its data haven't changed, so I don't refresh it". If the URL changes we change the key (in this PR), therefore flutter will say "oh there's a change, I have to refresh the widget".

[teolemon]

@monsieurtanuki very clear, and very glad to get rid of that very annoying bug.
I think this one is going to have a material impact on new user/contributor engagement.

[monsieurtanuki]

Thank you @teolemon for your review!
It was a very interesting issue - flutter-wise - and that will indeed give more credibility and relevancy to the app.