Enrich UT coverage for NetworkScanRequestTracker

Add test utilities for current and future test cases:
- Verify Messages send to client (through the Messenger)
- Turn on location and grant client fine location permission
- Emulate Network Scan result by capturing Messenger (and others)

Add more test cases to cover scenarios below:
- All messages should send to client on success/failure cases
- Network scan should stop on client process dies
- Resource should clean up and callback should unregister on
  stopped or interupted cases

Bug: 283308895
Test: atest NetworkScanRequestTrackerTest
Change-Id: Ie5cfb05d360e85f60b4b9ed3ae2ba93c1318e6cd