Box @Fetch* property wrappers in SwiftUI state when possible

[stephencelis]

There are some bugs with how the @Fetch* family of property wrappers behave when view identity throughout the hierarchy changes, forcing the Fetch* child value to be reconstructed in a bad state. E.g. a parent view might have some @State driving a @Binding in a child view that also has a @FetchAll, and changing that @State can cause the @FetchAll to be inert and not render in the view.

A fix for this has been to hold onto @FetchAll in @State, but nested property wrappers are cumbersome to use, and in Xcode 27 it's not even possible due to @State becoming a macro.

So instead, let's bake the @State directly inside the @Fetch*, preserving the data as the view hierarchy evolves.