Runs `cargo clippy --all-targets -- -D warnings` + `cargo test` inside
a rust:1.94-trixie container, then builds `rust/prop_grid_rs/Dockerfile`
and pushes three tags: the timestamped `main-<ts>-<sha>`, `latest`, and
a static `main` tag that `k8s/deployment-grid-rs.yaml` pins to.
Path-filtered to `rust/prop_grid_rs/**` so Elixir-only pushes don't
trigger a redundant Rust build.