fix(tests): split test_benchmark_matrix.py to clear the 500-line gate

[wesleyscholl]

Summary

• main's Konjo Gate (G4 · Complexity + Size + DRY, and the aggregate Konjo Gate — All Walls Clear) has been failing since PR bench: cold/unique 0%-reuse head-to-head — squish beats ollama on TTFT, decode, and E2E #211 merged, which grew tests/test_benchmark_matrix.py from 499 to 543 lines — over the 500-line new-violation limit and not in .konjo/oversized-allowlist.txt.
• Per project convention ("split them to remove, don't grow the list"), split the file along its own existing # ── section ── comment boundaries rather than allowlisting it:
  • tests/test_benchmark_matrix.py (288 lines): corpus, stats_ext, cache_probe
  • tests/test_benchmark_matrix_reporting.py (258 lines, new): memory, thermal, matrix_spec, host, cell pure helpers, report
• No behavior change — same 64 tests, same assertions, just regrouped. Verified passing (pytest -v, 64 passed) and clean under ruff check / ruff format --check.

Note: this PR does not touch the complexity-gate's 146 flagged functions (radon cc -n C) — that step has continue-on-error: true in the workflow, so it's cosmetic/non-blocking, not what's actually failing CI. Fixing that debt is a much larger, unrelated undertaking across ~20 files and is out of scope here.

Also found, not addressed in this PR: the scheduled Model Compression Pipeline workflow has been failing daily since at least 2026-07-02 — it calls dev/scripts/model_pipeline.py, which was intentionally deleted in a "scrub internal artifacts and private paths for public repo" commit. Fixing that requires a judgment call (retire the dead workflow vs. restore internal tooling to the public repo) that needs a maintainer decision, not a mechanical fix.

Test plan

• pytest tests/test_benchmark_matrix.py tests/test_benchmark_matrix_reporting.py -v — 64 passed
• ruff check / ruff format --check — clean
• Both files confirmed under 500 lines (288, 258)
• Reviewer: confirm CI goes green on this branch

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