Add paging and pull to refresh view states

[lmorda]

Linked Issue: Enable pull-to-refresh and pagination on the Contacts screen using mock contact data

Overview

This PR enhances the existing Contacts screen by introducing pull-to-refresh functionality and paging support using mock data.

All functionality continues to use mock data — no backend integration is included yet.

Changes Made

• ContactsScreen:

  • Added paging support and enabled pull-to-refresh using.
  • Displays a loading indicator at the bottom while new pages load.

• ContactsViewModel:

  • Introduced ContactsContract sealed interface to manage loading, success, and empty/error states.
  • Emits paged mock data and updates view state accordingly.

• HomeworkNextPageIndicator:

  • Moved to a shared UI package (ui/common) for reuse across features.

Tests Added

• ContactsViewModelTest:

  • Uses Jraska LiveData Testing to verify sequential view state emissions.

• ContactsScreenTest:

  • Verifies that pull-to-refresh and pagination update the contact list correctly.
  • Confirms that loading indicators appear as expected during interactions.

Notes

• All functionality in this PR uses mock data — no real data or network integration is performed.

[lmorda]

LGTM! Nice unit tests