chore(hk): verify Cargo lock freshness

[jrandolf]

Summary

• regenerate Cargo.lock in an isolated worktree during the slow hk profile
• fail when the committed lockfile is stale
• leave Cargo.lock unchanged

Validation

• exhaustive slow hk (including cargo-lockfile)\n- cargo test --locked -p sqlc-gen-sqlx --all-features --lib --test codegen (118 tests)