Add CachedService Class

This is a no-op refactoring. A new CachedService class is
introduced to better represent cached services and their expired
status. This class will be used to optimize expired service
removal in subsequent changes.

Bug: 387910548
Test: atest ConnectivityCoverageTests NsdManagerTest
Change-Id: I56fa43b8cc0c69d77aa14f0bdaf024a94c45757c
2 files changed