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 and ListView 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 not alter performance

⚠️ Unknown Walltime execution environment detected

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⚡ 10 improved benchmarks
❌ 9 regressed benchmarks
✅ 1562 untouched benchmarks
🆕 6 new benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	decompress_rd[f64, (10000, 0.1)]	109.2 µs	139.4 µs	-21.67%
❌	Simulation	decompress_rd[f64, (10000, 0.01)]	108.9 µs	139 µs	-21.67%
❌	Simulation	decompress_rd[f64, (10000, 0.0)]	108.9 µs	139 µs	-21.63%
❌	Simulation	decompress_rd[f32, (100000, 0.0)]	496.1 µs	583.7 µs	-15%
❌	Simulation	decompress_rd[f32, (10000, 0.1)]	78.2 µs	91 µs	-14.1%
❌	Simulation	decompress_rd[f32, (10000, 0.01)]	78.2 µs	90.7 µs	-13.83%
❌	Simulation	decompress_rd[f32, (10000, 0.0)]	78.7 µs	91 µs	-13.56%
❌	Simulation	patched_take_10k_contiguous_patches	259.6 µs	289.9 µs	-10.47%
❌	Simulation	patched_take_10k_random	272 µs	302.3 µs	-10.04%
⚡	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	chunked_varbinview_opt_canonical_into[(1000, 10)]	206.5 µs	170.5 µs	+21.15%
⚡	Simulation	take_10k_first_chunk_only	251.3 µs	208.9 µs	+20.29%
⚡	Simulation	take_10k_dispersed	264.8 µs	222.5 µs	+19.02%
⚡	Simulation	bitwise_not_vortex_buffer_mut[2048]	427.8 ns	369.4 ns	+15.79%
⚡	Simulation	chunked_varbinview_into_canonical[(100, 100)]	307.3 µs	273.6 µs	+12.34%
⚡	Simulation	patched_take_10k_adversarial	259.7 µs	231.3 µs	+12.28%
⚡	Simulation	patched_take_10k_first_chunk_only	282.9 µs	255.1 µs	+10.88%
⚡	Simulation	patched_take_10k_dispersed	297 µs	269.3 µs	+10.29%
🆕	Simulation	list_large	N/A	9.9 ms	N/A
...	...	...	...	...	...

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_{Comparing mk/list-length (12c7eea) with develop (9814173)}

[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