android: support Xiaomi rootless devices

[ousamabenyounes]

Summary

• Add Xiaomi, POCO, and Redmi to the Android 16+ rootless support allowlist.
• Extract rootless support checks into a pure predicate covered by unit tests.

Issues

Fix #658

Test verification (RED -> GREEN)

RED before implementation:

e: RootlessSupportTest.kt:28:20 Unresolved reference 'isRootlessSupported'.
e: RootlessSupportTest.kt:28:40 Unresolved reference 'ANDROID_16_SDK'.

GREEN with fix:

> Task :app:testFossDebugUnitTest
BUILD SUCCESSFUL

Revert proof:

RootlessSupportTest > android16XiaomiFamilyDevicesAreSupported FAILED
java.lang.AssertionError at RootlessSupportTest.kt:28
5 tests completed, 1 failed

Final checks:

./gradlew testFossDebugUnitTest --tests me.kavishdevar.librepods.utils.RootlessSupportTest
BUILD SUCCESSFUL

./gradlew assembleFossDebug
BUILD SUCCESSFUL