Record authoritative Linux comparison baseline

[tomsanbear]

Records the first authoritative cross-implementation Linux baseline.

Methodology:

• Exact Rust 1.97.0 toolchain (2d8144b7880597b6e6d3dfd63a9a9efae3f533d3)
• AMD Ryzen 9 7950X3D, pinned to CPU 0 on a V-cache CCD
• Performance governor enabled for the run and restored afterward
• Five Latin-square rotations, 50 samples per benchmark
• 1 second warmup and 2 second measurement windows

Validation:

• 110 CPU measurements and 60 allocation measurements
• Pinned core was 100% idle before every measured command
• Maximum audited system load was 1.12
• All allocation accounting and post-drop invariants pass
• Toolchain, compiler hash, host, commit, and comparison-pair metadata are embedded in the report

macOS is intentionally not included yet. The cross-platform aggregate visualizations will be generated only after a clean authoritative macOS run supplies the second half of the validated pair.

[codspeed-hq]

Merging this PR will not alter performance

✅ 110 untouched benchmarks

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_{Comparing bench/linux-1.97-baseline (22d96d4) with main (1f6e5f8)}