Optimize and clean up ScanManager

- Convert `UidImportance` to a record class
- Static import `ActivityManager.RunningAppProcessInfo` fields
- Define fields as final where possible
- Improve encapsulation

Bug: 394958283
Test: atest ScanManagerTest
Flag: Exempt refactor no-op
Change-Id: If0fc73f236c5bcf2e267df488e0e3b9d93ac84c2