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 degrade performance by 11.75%

⚠️ 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
❌ 4 regressed benchmarks
✅ 2203 untouched benchmarks
⏩ 293 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	decode_primitives[f32, (1000, 512)]	42 µs	64.2 µs	-34.63%
❌	Simulation	take_fsl_u32_random[16, 100]	125.9 µs	165.8 µs	-24.03%
❌	WallTime	dbp_assemble_kernel_avx512[(I128, 1024)]	463 ns	557 ns	-16.88%
❌	WallTime	dbp_assemble_kernel_avx2[(I128, 1024)]	464 ns	538 ns	-13.75%
⚡	Simulation	take_fsl_f16_random[16, 100]	179.5 µs	119.4 µs	+50.35%

Tip

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

---

_{Comparing fix/fastlanes-delta-validity-top-child (2d0a705) with develop (a542cbd)}

Footnotes

1. 293 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. ↩