Retry transient Gradle wrapper downloads

[amyu]

Summary

• enable Gradle Wrapper distribution download retries
• retry up to five times with exponential backoff starting at five seconds
• keep build and test failures outside the retry scope

Why

CI occasionally fails while downloading the Gradle distribution from services.gradle.org with transient errors such as Unexpected end of file from server and HTTP 503 responses. The Wrapper configuration currently disables its built-in download retry support.

Using the Wrapper's native retry settings applies consistently to Linux, Windows, and macOS without duplicating retry scripts across workflow jobs. The five-second initial delay doubles after each failed attempt, avoiding rapid repeated requests during a longer service interruption.

Validation

• ran ./sample-android-project/gradlew -p sample-android-project --version
• confirmed Gradle 9.6.1 loads the updated Wrapper configuration
• observed the Wrapper retrying distribution downloads in GitHub Actions
• git diff --check