fix: #1786 - safe write access to barcode lists

[monsieurtanuki]

Impacted file:

• dao_product_list.dart: safe write access to barcode lists

What

• There was a very hard to believe bug, with a concurrency exception (typically, a list being parsed while items are removed/added).
• This sounded crazy, because I expected each hive/get call to create a new object.
• With hive this is not the case, as all data are loaded at init, and we reuse the same objects.
• That explains the probability of concurrency exception: there are methods that list all items, other methods that add/remove items, and all of them may use the same object (loaded at init) at the same time.
• The solution was to be careful each time we add/remove items, with a safe copy of the list we intend to edit.
• I could not reproduce the bug btw.

Fixes bug(s)

Fixes: #1786
Fixes SMOOTHIE-V2

[M123-dev]

Looks like a really unlikely case. I can't say that this solves the problem but doesn't seem to add much complexity

[monsieurtanuki]

Thank you @M123-dev for your review!
I can't say either if it is 100% relevant, but I could not reproduce the bug (that did not happen often anyway) and I took me one hour to understand how a list that was only read could have a concurrency issue (answer: hive caches everything).