Build spark_size LargeList lengths as Int32 without Int64 cast #5272

What is the problem the feature request solves?

Follow-up from #5233
spark_size for LargeList reuses Arrow's length kernel, which returns Int64, then cast_with_options(..., Int32, safe: false), then (when nulls are present) to_vec() to patch null slots to -1. That is three allocations on the hot path.

On the array_size bench after #5233, LargeList (10% null) is only ~1.3x faster than main (7.54 µs vs 9.70 µs), while no-null List is ~12x. The gap is the Int64 → cast → copy chain, not the kernel idea itself.

Describe the potential solution

Build an Int32 length array straight from the LargeList i64 offset buffer (offsets[i+1] - offsets[i], with a checked conversion that errors on overflow rather than wrapping or becoming -1), then apply the same null →
-1 rewrite as the List path (null_count == 0 fast path; otherwise into_parts + set_indices).

Avoid allocating the intermediate Int64 length output and the Int32 cast result when those are only used to derive i32 sizes

Additional context

• Bench coverage already exists: spark_size: LargeList (10% null) in benches/array_size.rs. Consider adding a no-null LargeList shape for parity with the List production path.
• Keep safe: false / checked overflow semantics: a length that does not fit in i32 must error, not become null then -1
• Called out in review on perf: compute spark_size list lengths with Arrow length kernel #5233; left out of that PR so Map (Use the offset buffer for Map in spark_size #5266) and this path can land separately without blocking the List win