ci: Use Justfile targets in GitHub workflow and add missing v2024_7 feature

ci: Use Justfile targets in GitHub workflow and add missing v2024_7 feature

- Replace inline cargo fmt/clippy commands in rust.yml with just
  cargo-fmt-check and just cargo-clippy for consistency with local dev
- Make Justfile cargo-clippy use CARGO_PROJECT_FEATURES env var
  (defaults to v2022_6) so CI and local use share the same config
- Add missing v2024_7 feature to Cargo.toml to fix cargo doc failure
  caused by unexpected cfg condition

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>