Add list_length scalar function

[mhk197]

Adds a list_length scalar function returning the number of elements in each list of a List 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 12.62%

⚠️ 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.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 5 improved benchmarks
❌ 1 regressed benchmark
✅ 1577 untouched benchmarks
🆕 6 new benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_varbinview_into_canonical[(1000, 10)]	169 µs	205.5 µs	-17.78%
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	244.4 ns	186.1 ns	+31.34%
⚡	Simulation	bitwise_not_vortex_buffer_mut[1024]	304.7 ns	246.4 ns	+23.68%
⚡	Simulation	bitwise_not_vortex_buffer_mut[2048]	398.6 ns	340.3 ns	+17.14%
⚡	Simulation	chunked_varbinview_canonical_into[(100, 100)]	259 µs	224.4 µs	+15.39%
⚡	Simulation	chunked_varbinview_into_canonical[(100, 100)]	306.5 µs	271.1 µs	+13.05%
🆕	Simulation	list_large	N/A	10 ms	N/A
🆕	Simulation	list_medium	N/A	144.3 µs	N/A
🆕	Simulation	list_small	N/A	59 µs	N/A
🆕	Simulation	listview_large	N/A	6 ms	N/A
🆕	Simulation	listview_medium	N/A	98.3 µs	N/A
🆕	Simulation	listview_small	N/A	39.3 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 (51b1a4c) with develop (f1adef2)}

[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