General improvements for caching in TourStore

The TourStore currently relies on `.getTours()` to be called to populate the in-memory cache with all the objects. This can lead to bugs and hard-to-use APIs.

The TourStore API and functionality should be improved, either by refactoring it or not relying on it anymore. Some possible options:

1. Enable the browser cache for the REST endpoints and use that as the cache
2. Rely on an external library like @pinia/colada to handle the fetching.
3. Refactoring the existing TourStore API to improve usability