Delta validity is a top level child

[robert3005]

For performant delta encoding we have to read all the values in deltas
buffer that means that undefined values in deltas buffer are
significant. Instead of performing careful transformation dance to
ensure correctness we remove null values from deltas and keep them as
a top level child. Cascading encodings don't need any special handling
and will preserve all values since they're all valid.

[codspeed]

Merging this PR will improve performance by 10.47%

⚠️ Unknown Walltime execution environment detected

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

⚡ 1 improved benchmark
✅ 2094 untouched benchmarks
⏩ 518 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	words_gather_dispatch_neon[65536]	2.3 µs	2 µs	+10.47%

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 fix/fastlanes-delta-validity-top-child (81b248c) with develop (4435d5b)²}

Footnotes

1. 518 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. ↩

2. No successful run was found on develop (76381d5) during the generation of this report, so 4435d5b was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[joseph-isaacs]

https://github.com/vortex-data/vortex/actions/runs/37300373196