test: verify Arabic highlighting on Android runtime

[Khalid567-CPU]

Summary

Adds connected-device instrumentation coverage for ArabicHighlighter before publishing ArabicKit 0.2.0.

Included

• Configures AndroidJUnitRunner for :arabickit.
• Adds AndroidX instrumentation-test dependencies.
• Adds ArabicHighlighterInstrumentedTest.
• Verifies two yellow BackgroundColorSpan instances.
• Verifies that normalized search results map back to the expected original Arabic substrings, including diacritics and tatweel.

Required device verification

Run on a connected physical Android device:

.\gradlew.bat :arabickit:connectedDebugAndroidTest --no-daemon --console=plain --no-configuration-cache

This PR remains a draft until the connected test passes on the physical device.

Closes #5

[Khalid567-CPU]

Physical-device verification completed successfully on Infinix X6528 (Android 13): 1 instrumentation test passed. Final local verification also passed with connectedDebugAndroidTest, verifyFoundation, and :arabickit:assembleRelease; exit code 0 and clean working tree. GitHub Actions run #12 passed.