Refactor BatteryActivity to Controller and ViewModel architecture

Refactored BatteryActivity to discrete Controller > ViewModel > Activity
architecture. BatteryController hosts ProjectedDeviceController and listeners,
BatteryViewModel holds StateFlow data, and BatteryActivity renders Compose UI.

Test: ./gradlew :xr:projected:integration-tests:testapp:lintDebug
Test: ./gradlew :xr:projected:integration-tests:testapp:assembleDebug
Relnote: N/A
Change-Id: I5b32d3ed8644155ab5d4be5f34fc64cf7bba8107