Update navigation references and mock objects

[jleach]

In React Native, you should generally import from @react-navigation/native rather than @react-navigation/core.

The @react-navigation/native package provides the core utilities for navigation and is designed to be the main entry point for React Navigation. It includes essential components and hooks that you'll commonly use in your navigation setup, such as NavigationContainer, useNavigation, and useRoute.

On the other hand, @react-navigation/core is a lower-level package that @react-navigation/native depends on. It's not typically used directly unless you need to extend or modify the core behaviour of React Navigation.