Summary

• Add a determinism contract test for the cu-caterpillar example, gated behind a new determinism_ci feature.
• Wire the determinism test into CI (debug workspace only) and into just std-ci for local runs.

Related issues

• Closes add a deterministic non-regression test in CI #728

Changes

• New determinism test builds a sim-mode app, records two runs, replays copperlists, and compares bincode-encoded streams to enforce record/resim equality; it writes under target/determinism_tests and cleans up on success.
• examples/cu_caterpillar/Cargo.toml adds determinism_ci, and examples/cu_caterpillar/src/main.rs conditionally includes the test module under #[cfg(all(test, feature = "determinism_ci"))].
• CI and justfile run the test single-threaded with fixed env (RAYON_NUM_THREADS=1, COPPER_DETERMINISM_ITERS=256,COPPER_DETERMINISM_DT_TICKS=1000) for stability.

Testing

• just std-ci
• just lint
• cargo +stable nextest run --workspace --all-targets
• RAYON_NUM_THREADS=1 COPPER_DETERMINISM_ITERS=32 COPPER_DETERMINISM_DT_TICKS=1000 cargo test -p cu-caterpillar --features determinism_ci -- determinism_record_and_resim --test-threads=1

Checklist

• I have updated docs or examples where needed
• I have added or updated tests where needed
• I have considered platform impact (Linux/macOS/Windows/embedded)
• I have considered config/logging changes (if applicable)
• This change is not a breaking change (or I documented it below)