Add caching for Android SDK, Gradle, and Expo prebuild

[markwatson]

Summary

This PR adds GitHub Actions caching for Android build dependencies and generated files across all CI/CD workflows (build, release). This reduces build times by avoiding redundant downloads and regeneration of Android SDK packages, Gradle dependencies, and Expo prebuild artifacts.

Key Changes

• Android SDK Caching: Added caching for ~/.android/sdk to avoid re-downloading SDK packages on each workflow run
• Expo Prebuild Caching: Added caching for the generated android/ directory with cache invalidation based on app.json, package-lock.json, and module changes
• Gradle Caching: Added caching for Gradle caches and wrapper to speed up Android builds
• Conditional Prebuild: Modified the "Generate Android project" step to only run when the prebuild cache is not hit, avoiding unnecessary regeneration
• Applied to All Workflows: Implemented consistent caching strategy across build.yml and release.yml workflows

Implementation Details

• Cache keys are based on runner OS and relevant file hashes to ensure cache invalidation when dependencies or configuration changes
• Gradle cache includes restore keys for partial cache hits across different dependency versions
• Each workflow job has its own cache ID to prevent conflicts between test and build jobs

https://claude.ai/code/session_01UttwqGKARJaHeoWyV8J6kA