perf: characterize rational row-clearing allocation costs

[acgetchell]

• Add small and wide-component rational benchmark fixtures across D=2–8.
• Isolate component cloning and integer scaling costs from complete determinant, sign, and solve operations.
• Publish allocation and timing data with provenance and reproduction steps supporting the existing borrowed implementation.

Closes #233

Summary by CodeRabbit

• Performance

  • Added expanded rational-arithmetic benchmarks covering small and wide inputs.
  • Added allocation-focused measurements for determinant, solving, and row operations.
  • Added validation to confirm benchmark results remain mathematically correct.

• Documentation

  • Documented the scope and interpretation of wide rational-input benchmarks.
  • Added a performance study comparing allocation behavior and timing across representative workloads.
  • Clarified which benchmark groups contribute to release performance reports.

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📥 Commits

Reviewing files that changed from the base of the PR and between 25aa4c0 and 2688964.

⛔ Files ignored due to path filters (4)

• Cargo.lock is excluded by !**/*.lock
• docs/assets/rational-row-clearing-allocations.csv is excluded by !**/*.csv
• docs/assets/rational-row-clearing-timings.csv is excluded by !**/*.csv
• uv.lock is excluded by !**/*.lock

📒 Files selected for processing (8)

• Cargo.toml
• benches/common/rational.rs
• benches/exact.rs
• docs/BENCHMARKING.md
• docs/performance/rational-row-clearing.md
• justfile
• pyproject.toml
• tests/rational_allocations.rs

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📝 Walkthrough

Walkthrough

The change adds shared validated rational fixtures for small and wide inputs, expands exact benchmarks across input families and dimensions, adds allocation-evidence tests, updates development-tool pins, and documents benchmark scope and row-clearing measurements.

Changes

Rational performance evidence

Layer / File(s)	Summary
Validated rational fixtures and Gaussian references benches/common/rational.rs	Adds deterministic rational input families, validated matrix and vector accessors, exact matrix-vector multiplication, and pivoting Gaussian determinant and solve references.
Expanded exact benchmark coverage benches/exact.rs	Moves shared helpers into rational_bench, uses validated fixture accessors, and runs rational benchmarks for all input families across dimensions 2–8.
Allocation measurement tests and tooling tests/rational_allocations.rs, Cargo.toml, justfile, pyproject.toml	Adds feature-gated allocation measurements for rational operations and updates the allocation-counter, rumdl, and semgrep development pins.
Benchmark scope and study record docs/BENCHMARKING.md, docs/performance/rational-row-clearing.md	Documents canonical and diagnostic benchmark groups and records allocation, timing, reproduction, environment, and validation results.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 26889

The benchmark fixtures, allocation measurements, and supporting tooling changes do not leave a concrete unresolved merge risk.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The benchmark fixtures, allocation test, documentation, and allocation-counter dependency support issue #233. The rumdl update in justfile and the semgrep update in pyproject.toml are tooling-…	Remove the unrelated rumdl and semgrep pin updates, or provide a linked requirement that explains why those updates are necessary for this pull request.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: characterizing allocation costs in rational row clearing.
Linked Issues check	✅ Passed	The changes address issue #233 by adding D=2–8 rational benchmarks, representative and wide inputs, independent exact-result validation, allocation measurements, timing evidence, and reproduction docu…

Full details: Out of Scope Changes check

Explanation

The benchmark fixtures, allocation test, documentation, and allocation-counter dependency support issue #233. The rumdl update in justfile and the semgrep update in pyproject.toml are tooling-pin changes with no stated connection to the issue objectives.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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• Create PR with unit tests
• Commit unit tests in branch feat/233-row-clearing

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.00%. Comparing base (25aa4c0) to head (2688964).
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Coverage   98.00%   98.00%           
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  Files          13       13           
  Lines        6579     6579           
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  Hits         6448     6448           
  Misses        131      131           

Flag	Coverage Δ
unittests	98.00% <ø> (ø)

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