Optimize and clean up PeriodicScanManager.java

- Convert inner class to record where possible
- Improve encapsulation
- Use stream() for more elegant search functions

Bug: 394958283
Test: atest PeriodicScanManagerTest
Flag: Exempt refactor no-op
Change-Id: I4653a4d236bbd20d450f9050f3487a824ebc1aca