Shared state

[mbrandonw]

This PR builds upon #200 (which we will merge soon) in order to start making use of @Shared throughout the code base. The main thing left to do is fix tests.

[lukeredpath]

Just an FYI, but after experimenting with this approach of wrapping some shared state in a property wrapper in my app I did find a serious issue with this initializer - it can trigger an infinite view body render loop if invoked from a view body.

This can be easily done, for example if you have some child feature that uses it:

@Reducer
struct Child {
  struct State: Equatable {
    @ObservationStateIgnored @ServerConfig_ var config
  }
}

Then you initialize the child state in a view (e.g. to pass to NavigationLink(state:)), and that view's state also uses the property wrapper, this causes the property wrapper on the child to initialize, which in term updates the shared state, which triggers the parent view to update, which calls body and the loop begins.

I think its better to provide just an empty initializer.