[codex] Fix clippy node role label iteration

[GatewayJ]

Type of Change

• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Refactor
• Other:

Related Issues

N/A

Summary of Changes

Fixes the clippy iter_kv_map warning reported by CI with Rust/clippy 1.95.

The node role label extraction now iterates over map keys directly with labels.keys() instead of iterating key-value pairs and ignoring the values.

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Passed make pre-commit (fmt-check + clippy + test + console-lint + console-fmt-check)
• Added/updated necessary tests (N/A: lint-only code cleanup)
• Documentation updated (if needed) (N/A)
• CHANGELOG.md updated under [Unreleased] (if user-visible change) (N/A)
• CI/CD passed (if applicable)

Impact

• Breaking change (CRD/API compatibility)
• Requires doc/config/deployment update
• Other impact: restores compatibility with newer clippy warnings treated as errors

Verification

make pre-commit

Additional Notes

This follows up on the CI failure observed in PR #115 after GitHub Actions used Rust/clippy 1.95.

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