Fix public CI clippy baseline

[luca-ctx]

Summary

• make the import error-summary root-cause iterator clippy-clean
• rewrite the clustered fast-path test branch as an explicit ordering match

Validation

• RUSTUP_TOOLCHAIN=1.86.0 cargo clippy --workspace --all-targets --locked -- -D warnings
• bash scripts/check.sh -- test //:cargo_clippy //:source_diff_check --config=ci
• full local public gate passed before this follow-up: bash scripts/check.sh --mode=ci (18/18 targets)