ScanManager: Direct handler access

The handler should not be erased by the test, as the test is already
providing the looper to build it.
Also shortcut some serialiation that was only bringing obfuscation

Bug: 330956986
Fix: 330956986
Bug: 380539632
Bug: 380510617
Bug: 380510672
Bug: 380536618
Bug: 380510672
Bug: 380510672
Bug: 380536573
Bug: 378542424
Bug: 346028665
Bug: 347474468
Test: atest ScanManagerTest --rerun-until-failure 3000
Flag: TEST_ONLY || The change in app are no-op
Change-Id: I7e1a13b036a1a4ef9fddf154637d3ff931db3cb0