[cortinico]

Summary

• Add ./gradlew format and ./gradlew formatCheck for every Java source in SoLoader, using pinned Google Java Format 1.25.2 downloaded by Gradle. No formatter binary is committed.
• Add a format GitHub Actions job that checks Java formatting.
• Document the same commands for standalone and fbsource checkouts.

Follow-up to #156. This PR is based on its branch so the diff contains only formatting setup; it can be retargeted to main after #156 merges.

Test plan

• ./gradlew format — passed; the 66 existing Java files already conform to the pinned formatter.
• ./gradlew formatCheck — passed.
• Temporarily introduced a formatting error in a Java file: formatCheck failed as expected, and format restored the file. No source-file changes remain.
• git diff --check — passed.
• GitHub Actions — both format and build jobs passed.

Changelog

• Internal: developer tooling only.