[CHORE] cargo fmt --check not enforced in CI — code formatting can drift undetected

Summary

The CI pipeline (.github/workflows/ci.yml) runs cargo clippy and cargo test but never runs cargo fmt --check. This means code formatting can drift across PRs without any automated gate.

Current CI Lint Job

- name: Run clippy (fail fast on errors)
  run: cargo clippy --workspace --all-features -- -D errors

cargo fmt --check is absent.

Impact

• Inconsistent formatting accumulates over time, making diffs harder to read
• Contributors may submit unformatted code that passes CI
• Code review effort is wasted on style discussions that rustfmt would resolve automatically

Suggested Fix

Add a formatting check step to the lint job in ci.yml:

- name: Check formatting
  run: cargo fmt --all -- --check

This is a one-line addition that runs in seconds and prevents formatting drift entirely.