* Add sessions overview UI tests
* Expose static methods from the UserSession name and lastActivity formatters; cleaned up the UserSessionsOverview a bit
* Add UserSessionsOverviewViewModel unit tests
* Add UserSessionsOverviewService unit tests
Adds the test targets for Unit and UI tests
Adds mock screen data and utilities to render each mock screen for previews/ui tests.
Changes Published property in the service to CurrentValueSubject. we don't need the synthesized aspect of Published and property wrappers cannot be included in protocols.
