Introduce NavigationStackBound as a fix for unpredictable ContainerLifecycle calls

[killlilwinters]

Description

This merge request introduces a dedicated NavigationStackBound SwiftUI wrapper to fix unstable NavigationStack behavior when the navigation path is exposed from UDF state through reconstructed Binding(get:set:) instances.

The issue occurs because NavigationStack is sensitive to binding identity. When a container remaps the path binding on every state update, SwiftUI may re-traverse the navigation tree during active transitions, causing unintended descendant lifecycle effects such as duplicate @StateObject initialization and incorrect onContainerDidLoad / onContainerDidUnload calls.

Instead of moving navigation state ownership away from UDF, this approach keeps the external binding as the source of truth and stabilizes only the binding presented to NavigationStack. The alternative would have been to redesign navigation ownership or add explicit synchronization flags, but this solution isolates the problem at the view boundary with minimal impact on existing state flow.

Changes Made

• Added new NavigationStackBound<Root: View> component in UDF/View/Router/NavigationStackBound.swift.
• Wrapped an external Binding<NavigationPath> with:
  • @Binding private var external
  • @State private var local
• Seeded local state from the external path during initialization so restored/deep-linked navigation appears immediately without an empty initial stack.
• Rendered NavigationStack using the stable local binding:

  NavigationStack(path: $local) {
      root()
  }

• Added two-way synchronization between external and local paths using equality guards to prevent update loops:

  .onChange(of: external) { newExternal in
      guard local != newExternal else { return }
      local = newExternal
  }
  .onChange(of: local) { newLocal in
      guard external != newLocal else { return }
      external = newLocal
  }

• Documented the failure mode, synchronization model, usage pattern, and an important requirement that the owning container scope must include the form that stores the navigation path.