chore: pin current Rust security tools

[AnthonyRonning]

Summary

• add a separately pinned current nixpkgs input for cargo-audit, cargo-deny, and cargo-machete in the development shell
• keep the application, Nitro, kernel, and primary nixpkgs build inputs unchanged
• run CI clippy and tests with --locked so Cargo.lock cannot drift silently

Why

The primary August 2025 nixpkgs pin provides cargo-audit 0.21.2, which cannot parse current RustSec advisories containing CVSS 4 data. A dev-only security-tool pin provides a current parser without moving reproducibility-sensitive build inputs.

Validation

• git diff --check
• workflow YAML parse
• nix flake check --no-build --all-systems
• nix develop exposes cargo-audit 0.22.2, cargo-deny 0.20.2, and cargo-machete 0.9.2
• cargo audit fetched and parsed the current RustSec database successfully
• cargo fmt --all -- --check
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --locked --all-features: 213 passed, 16 ignored
• verified every pre-existing flake.lock node is unchanged; only the security-tools-nixpkgs node and root input edge were added

Scope

This does not add an audit CI job or cargo-deny policy, and does not update the primary nixpkgs or Nitro inputs.

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Review details

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 95b29a8a-61ec-4c13-b095-e1b690a941ad

📥 Commits

Reviewing files that changed from the base of the PR and between a3ecc93 and 37261d1.

⛔ Files ignored due to path filters (1)

• flake.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• .github/workflows/rust.yml
• flake.nix

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex-opensecret-supply-chain-guardrails-opensecret

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.