Improve update collection mechanism for sync v3

- [ ] BaseMappedList updater should use UpdateAction to be able to replace the existing mapped value (or update, or swallow do update)
- [ ] TemplateView needs to resubscribe on `update()` and support replacing the view model with another.
- [ ] If sync v3 updates perf seems problematic, either of these may be a solution:
- properly implement the `reset` event on collections
- consider a bulk update mechanism for observable collections.
- [ ] other lazylistviews have shown some friction by not having random access. We could add a method to create an iterator at a given index.