bench: compare uniform and per-chunk bitpacking

[mhk197]

Add a benchmark sweep comparing global-width and per-chunk encoding and decoding across uniform, alternating, drifting, and outlier-heavy distributions. Report packed sizes alongside timing to make compression and runtime tradeoffs visible.

Part 9/9 of the bitpacked-v2 stack (260 added + removed lines). Merge in order; each draft targets the preceding branch, starting from develop.

1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9

Validation: 431 FastLanes/BtrBlocks tests passed (1 skipped), along with 4 FastLanes doctests. Focused Clippy passed with --all-targets --all-features -- -D warnings. Changed Rust files were formatted with nightly; git diff --check passed.

GPU execution was not tested. CUDA validation and workspace-wide all-feature Clippy were previously blocked by the nvCOMP 5.1 SDK download in this environment.

The benchmark smoke test (--profile dev -- --test) passed before the serde extraction; this follow-up only relocates wire-format handling and adds the boundary regression.

[codspeed]

Merging this PR will regress 1 benchmark

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 3 improved benchmarks
❌ 1 regressed benchmark
✅ 2249 untouched benchmarks
🆕 160 new benchmarks
⏩ 218 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	random_i8[0.5]	72.4 µs	96 µs	-24.59%
⚡	Simulation	random_i16[0.95]	99.7 µs	81.5 µs	+22.34%
⚡	WallTime	mul_i16_nonnull_avx512	8.1 µs	7.1 µs	+13.57%
⚡	WallTime	mul_i32_nonnull_avx512	7.9 µs	7.1 µs	+10.58%
🆕	Simulation	compress_v1[u16, drift]	N/A	295.8 µs	N/A
🆕	Simulation	compress_v1[u16, drift+exc1%]	N/A	832.8 µs	N/A
🆕	Simulation	compress_v1[u16, drift+null10%]	N/A	523.6 µs	N/A
🆕	Simulation	compress_v1[u16, random]	N/A	300.6 µs	N/A
🆕	Simulation	compress_v1[u16, spiky]	N/A	888.4 µs	N/A
🆕	Simulation	compress_v1[u16, spiky+exc1%]	N/A	896.9 µs	N/A
🆕	Simulation	compress_v1[u16, uniform]	N/A	272.5 µs	N/A
🆕	Simulation	compress_v1[u16, uniform+exc1%]	N/A	814.7 µs	N/A
🆕	Simulation	compress_v1[u16, uniform+null10%]	N/A	500.3 µs	N/A
🆕	Simulation	compress_v1[u16, zero_heavy]	N/A	272.4 µs	N/A
🆕	Simulation	compress_v1[u32, drift]	N/A	432.2 µs	N/A
🆕	Simulation	compress_v1[u32, drift+exc1%]	N/A	992.5 µs	N/A
🆕	Simulation	compress_v1[u32, drift+null10%]	N/A	1.5 ms	N/A
🆕	Simulation	compress_v1[u32, random]	N/A	432.4 µs	N/A
🆕	Simulation	compress_v1[u32, spiky]	N/A	1 ms	N/A
🆕	Simulation	compress_v1[u32, spiky+exc1%]	N/A	1 ms	N/A
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing mk/bitpacked-stack-09-benchmarks (4cc3a9d) with mk/bitpacked-stack-08-fused-encoder (910328c)}

Footnotes

1. 218 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩