Add list_length scalar function

[mhk197]

Adds a list_length scalar function returning the number of elements in each list of a List-like array.

• Computed purely from the list's offsets/sizes — it never reads elements. Different paths for List, ListView, and FixedSizeList arrays.
• Returns a U64 array; a null list yields a null length.
• Registered as a built-in (vortex.list.length) alongside list_contains, and exposed via the list_length(expr) expression constructor.

[codspeed-hq]

Merging this PR will improve performance by 18.65%

⚠️ 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.

⚡ 6 improved benchmarks
❌ 1 regressed benchmark
✅ 1582 untouched benchmarks
🆕 6 new benchmarks
⏩ 4 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	slice_empty_vortex	339.4 ns	397.8 ns	-14.66%
⚡	Simulation	chunked_bool_canonical_into[(1000, 10)]	27.2 µs	15.8 µs	+71.66%
⚡	Simulation	copy_nullable[65536]	1.4 ms	1 ms	+32.02%
⚡	Simulation	copy_non_nullable[65536]	1,089.2 µs	908.5 µs	+19.89%
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	215.3 ns	186.1 ns	+15.67%
⚡	Simulation	bitwise_not_vortex_buffer_mut[1024]	275.6 ns	246.4 ns	+11.84%
⚡	Simulation	eq_i64_constant	318.6 µs	288.7 µs	+10.34%
🆕	Simulation	list_length_large	N/A	10 ms	N/A
🆕	Simulation	list_length_medium	N/A	142.5 µs	N/A
🆕	Simulation	list_length_small	N/A	57.7 µs	N/A
🆕	Simulation	listview_length_large	N/A	6 ms	N/A
🆕	Simulation	listview_length_medium	N/A	97.2 µs	N/A
🆕	Simulation	listview_length_small	N/A	37.8 µs	N/A

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/list-length (8ac3a23) with develop (3451cb0)}

Footnotes

1. 4 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. ↩

[gatesn]

May as well support FixedList as well, then implement reduce to collapse it into the constant

[mhk197]

Implemented reduce for nonnullable fsl, delegated nullable to execute since we can't easily get validity (talked offline)

[gatesn]

You should define a enum AnyListView { List(...), FixedList(...) } , then you can just match on it above in the execute_until

[mhk197]

do we want to execute FixedList? We can just get the size from the dtype

[gatesn]

You're not executing the FixedList itself, you're basically saying, run execution one step at a time until it matches one of these encodings.

So there may be some scalar function that happens to return a FixedList, then you will terminate and have access to it

[mhk197]

Discussed offline -- execute_until may need refactor to return Match instead of discarding it