chore: update launchdarkly-android-client-sdk to 5.12.0

[kinyoklion]

Summary

Update launchdarkly-android-client-sdk from pinned version 5.11.1 to 5.12.0 (the latest release).

The 5.12.0 release removes the Kotlin stdlib dependency from the SDK itself, making it a lighter dependency for Java-only projects. No API changes or deprecations.

Review & Testing Checklist for Human

• Build the project with ./gradlew assembleDebug to verify it compiles
• Run the app on an Android device/emulator and verify flag evaluation works

Notes

• The version constraint pattern remains pinned to an exact version as before
• No deprecated API usage was found in the example code
• The SDK changelog: https://github.com/launchdarkly/android-client-sdk/releases/tag/5.12.0

Link to Devin session: https://app.devin.ai/sessions/54f519e98f9c415cb2bb949c0888e8a1
Requested by: @kinyoklion

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