Add roaring64 BSI comparison and batch value APIs

[guymolinari]

Description

This PR adds focused roaring64 BSI APIs and optimizations for comparison-heavy workloads. It keeps existing public method signatures intact while adding faster paths for BSI-to-BSI comparisons, aligned batch value extraction, and fused batch equality/value extraction.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement
• Code refactoring
• Documentation update
• Test improvements
• Build/CI changes

Changes Made

What was changed?

• Added roaring64 BSI-to-BSI comparison support for same-column comparisons.
• Added aligned batch value extraction so callers can retrieve many BSI values without repeated row-by-row lookups.
• Added BatchEqualValues, which returns matched column IDs with their matched int64 values in one pass, optionally restricted by a found set.
• Refactored the optimized int64-width BatchEqual path to share the same trie/cube matching logic used by BatchEqualValues.
• Preserved generic fallback behavior for wider-than-int64 BSI values.
• Added correctness tests for signed values, found sets, duplicate query values, big-width fallback, and result isolation.
• Added benchmark notes in roaring64/BSI_BENCHMARKS.md.

Why?

These APIs avoid common row-by-row GetValue / GetBigValue loops in BSI workloads. In downstream query-engine validation, the fused BatchEqualValues path removed a second lookup pass from relationship-vector reduction and reduced a representative join reduction case from roughly the 480ms band to roughly 288ms median.

Validation

• go test ./roaring64 -count=1
• go test ./... -count=1
• go test ./roaring64 -run '^$' -bench 'BenchmarkBSI64BatchEqual.*LargeFixture' -benchmem -benchtime=2s -count=5
• go test ./roaring64 -run '^$' -bench 'BenchmarkBSI64CompareBSISameRow' -benchmem -count=5

Downstream smoke validation with a local workspace override:

• GOWORK=/tmp/qs-roaring.work go test ./qsruntime -count=1
• Standard TPC-H query suite passed against QuantaStream.
• Representative q5.060_combined_graph_regional_count median improved to about 288ms from the prior ~480ms band.

Representative Results

See roaring64/BSI_BENCHMARKS.md for benchmark commands and fuller notes.

On the large batch-equality fixture:

• BatchEqualValues: about 1.6-2.3ms/op
• BatchEqual + GetBigValues: about 5.4-7.1ms/op
• BatchEqual + GetValue loop: about 10.9-13.0ms/op

Compatibility

• Existing public method signatures are unchanged.
• New APIs are additive.
• Wider-than-int64 BSI values continue to use generic fallback paths.
• BatchEqualValues result order is intentionally unspecified.

[guymolinari]

@lemire - Are you good with this?