perf(arrow/array): compare boolean values by valid runs

[fallintoplace]

What

• compare all-valid Boolean value bitmaps in bulk
• compare nullable values one valid run at a time
• keep tiny runs and fragmented validity on the scalar path
• ignore physical value bits under null slots

Boolean values are already bit-packed, but equality currently extracts the left and right value bit for every valid row.

The C++ equality path uses the same general shape: scalar comparison for tiny runs and bitmap comparison for larger runs.

https://github.com/apache/arrow/blob/485499fd02ea2b0c323d67871fbe96aae4232504/cpp/src/arrow/compare.cc#L279-L313

Benchmark

Apple M1 Pro, Go 1.26.3. Representative medians from five runs:

Case	Before	After	Change
65K all valid, equal	401 us	219 us	-45%
65K clustered 10% null, equal	395 us	225 us	-43%
65K alternating null, equal	340 us	331 us	-3%
1M all valid, equal	6.12 ms	3.56 ms	-42%
1M clustered 10% null, equal	6.04 ms	3.66 ms	-39%
1M unaligned slice, equal	6.15 ms	3.51 ms	-43%

The fragmented-run probe keeps periodic and alternating null patterns near the existing scalar cost.

Tests

• go test -race ./arrow/array -count=1
• go vet ./arrow/array
• go test ./...