perf(arrow/array): bulk append list nulls and empty values

[fallintoplace]

What

• reserve List and ListView batches once
• update parent validity in bulk
• append repeated offsets and zero sizes through the unsafe builder path
• cover List, LargeList, ListView, and LargeListView

These bulk APIs currently call the scalar append path once per list slot. Empty and null variable-sized lists do not append child values, so only the parent validity and dimensions need updating.

This follows the batching shape used by the C++ list builders:

https://github.com/apache/arrow/blob/485499fd02ea2b0c323d67871fbe96aae4232504/cpp/src/arrow/array/builder_nested.h#L138-L160

For ListView, this keeps Go's current physical representation by repeating the current child offset with a zero size.

Benchmark

Apple M1 Pro, Go 1.26.3. Representative medians from three to five runs with 65,536 slots:

Builder	Operation	Before	After	Change
List	nulls	848 us	201 us	-76%
List	empty	848 us	197 us	-77%
LargeList	nulls	1.08 ms	241 us	-78%
LargeList	empty	1.05 ms	245 us	-77%
ListView	nulls	1.35 ms	414 us	-69%
ListView	empty	1.24 ms	415 us	-67%
LargeListView	nulls	1.47 ms	509 us	-65%
LargeListView	empty	1.50 ms	505 us	-66%

Regular-list allocations drop from 45 to 18 per batch. List-view allocations drop from 68 to 25. The n=1 cases stay within benchmark noise.

Tests

• go test ./arrow/array -count=1
• go test -race ./arrow/array -run 'TestListBuilderBulkAppendNullsAndEmptyValues|TestList|TestLargeList' -count=1
• go vet ./arrow/array
• go test -p 1 ./...