chore: migrate proxy benchmarks to Gungraun

[mjc]

Summary

• replace the removed IAI benchmark dependency with Gungraun
• provide the pinned Gungraun runner in the Nix development shell
• keep instruction, branch, cache, and Divan measurements available

Evidence

• formatting check passed
• clippy with all features and warnings denied passed
• proxy benchmark targets compile
• Gungraun classifier benchmark completed without regressions
• Divan 16-request window median: 102.8 ns

All commits are GPG-signed.

Summary by CodeRabbit

• Performance

  • Improved request serialization benchmarking to measure more efficient reuse of shared output buffers across multiple requests.
  • Continued coverage of cache, request classification, and client-socket round-trip performance scenarios.

• Developer Experience

  • Updated Callgrind-based benchmarking support to use Gungraun.
  • Added Gungraun runner support to the development environment and refreshed dependency-audit coverage.

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⚙️ Run configuration

Configuration used: Repository UI (base), Organization UI (inherited)

Review profile: ASSERTIVE

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Run ID: 436b3b49-13f5-49ae-8d05-201f7a3daefd

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Reviewing files that changed from the base of the PR and between 1e516c2 and ba80f2f.

📒 Files selected for processing (1)

• benches/cache_miss_roundtrip_callgrind.rs

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⚙️ Run configuration

Configuration used: Repository UI (base), Organization UI (inherited)

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 1c09c50f-05d1-4c7a-ab35-e4d42b8ba334

📥 Commits

Reviewing files that changed from the base of the PR and between 145b36c and 1e516c2.

⛔ Files ignored due to path filters (1)

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

📒 Files selected for processing (6)

• Cargo.toml
• benches/cache_miss_roundtrip_callgrind.rs
• benches/request_classifier_callgrind.rs
• benches/request_serialization.rs
• flake.nix
• scripts/audit-advisories

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📝 Walkthrough

Walkthrough

The PR replaces iai-callgrind with gungraun, packages the Gungraun runner in the development shell, updates advisory tracking, and adds batched request serialization benchmarking.

Changes

Benchmark migration

Layer / File(s)	Summary
Gungraun tooling and dependency setup Cargo.toml, flake.nix, scripts/audit-advisories	The development dependency, runner package, development shell, and advisory tracking now use Gungraun.
Callgrind benchmark framework migration benches/cache_miss_roundtrip_callgrind.rs, benches/request_classifier_callgrind.rs	The benchmarks import Gungraun APIs. The cache benchmark also sets a recursion limit of 256.
Batched request serialization benches/request_serialization.rs	Serialization separates clearing from appending. A 16-request window benchmark reuses one sink and clears it once.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 1e516

The benchmark migration and added serialization benchmark have no remaining concrete merge-blocking risk in the supplied evidence.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main change: migrating proxy benchmarks from IAI to Gungraun.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (3 skipped: 3 u…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/gungraun-benchmarks

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