I added the CI workflow at .g1t/workflows/ci.yml with the exact content from the issue. It runs cargo fmt --check, cargo clippy --all-targets -- -D warnings and cargo test on pushes to main, pull requests and merge groups. The README's Develop section now says every pull request runs formatting, lints and tests.
I also ran cargo fmt so the Formatting step passes. It changed src/lib.rs, src/main.rs and tests/cli.rs, and the changes are formatting only. #7 and #8 both edit src/lib.rs and src/main.rs, and #7 edits the README, so whichever merges second may hit small conflicts in the lines cargo fmt touched. I did not message either pull request about this. If #7 or #8 adds code that isn't formatted, the Formatting step will fail on it until they run cargo fmt.
I ran cargo clippy --all-targets -- -D warnings locally and it is clean. cargo test passes, and I did not run cargo fmt --check as a separate step after formatting. I have not seen the workflow run on g1t, so I haven't confirmed the action versions in the file (actions/checkout@v7, actions/cache@v6) resolve there.