Feat: Real-time sync shopping lists addition/removal

[RedX2501]

Add real-time synchronization to shopping lists

Adding or removing shopping lists now immediately
updates them in the available shopping list selector
in the "add items" overview.

I'm not entirely sure if calling refresh() is enough. At least in my tests it was but I'm not sure if there are side-effects missing that I don't know about.

When you use the Linux or Android App and have Chrome open at the same time the update in Chrome happens once the window has focus. Not sure what that is about.

Again this PR is only a draft as it depends on other PRs. I'll rebase onto main once those are complete.

[TomBursch]

I'm not entirely sure if calling refresh() is enough. At least in my tests it was but I'm not sure if there are side-effects missing that I don't know about.

Yeah, that's fine. Also, thanks for the refactor.

I know this is a draft, but in general, I'd recommend branching from main, since this PR doesn't really depend on the other changes. This saves you some time when changes have to be made in other PRs (and you won't need to update this branch because of that) and makes it a bit easier to review, and we could have merged this already 😉

[RedX2501]

Yeah, at first glance it does not depend but on my dev side it does because of the changes on the launch.json (which keeps giving me git errors when changing branches due to being overwritten on the checkout of the other branches). Maybe I'll just be more patient in the future with opening these PRs.

[TomBursch]

Looks good, I noticed the off methods are missing. If you add those, then I'll approve this.

[RedX2501]

I didn't add them as nobody uses them. So there would be less API to test later.

[TomBursch]

They are used inside the close method of the cubit.

@override
  Future<void> close() async {
    ApiService.getInstance().offShoppinglistItemAdd(onShoppinglistItemAdd);
    ApiService.getInstance().offShoppinglistItemRemove(onShoppinglistItemRemove);
    super.close();
  }

If you switch households, for example, the cubit is closed but would remain a listener on the socket events. This would result in errors and a memory leak, since it couldn't be garbage collected.