Prepare benchmark-specific data formats

[palaska]

data-gen now calls each benchmark's prepare_format hook after standard conversions. This creates benchmark-specific formats through vx-bench prepare-data.

Validation:

• cargo +nightly fmt --all --check
• cargo clippy -p vortex-bench --all-targets --all-features -- -D warnings

Agent: Codex.

[codspeed]

Merging this PR will improve performance by 52.75%

⚠️ 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.

⚡ 1 improved benchmark
✅ 2186 untouched benchmarks
⏩ 218 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	arrow_checked_add_u32_neon[16384]	20.4 µs	13.4 µs	+52.75%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing bp/fix-data-gen-format-preparation (1873df3) with develop (bffdca1)}

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. ↩

[github-actions]

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