feat: SQL COUNT(DISTINCT column) support via HyperLogLog Sketch

[akanksha-akkihal]

Summary
Support SQL queries of the form:
SELECT srcip, COUNT(DISTINCT dstip) AS unique_peers FROM netflow_table WHERE time BETWEEN DATEADD(s, -11, NOW()) AND DATEADD(s, -10, NOW()) GROUP BY srcip

This should work end-to-end through ASAPQuery’s precompute/streaming engine using a HyperLogLog (HLL) sketch (asap_sketchlib::HllSketch).

The implementation should:

• Support approximate distinct counting via HLL
• Integrate with the precompute pipeline
• Be configurable via versioned inference + streaming configs

Current Status
COUNT(DISTINCT column) is is currently not supported in the streaming/precompute path, due to gaps across multiple layers:

Layer	Gap
SQL parser	DISTINCT inside COUNT is ignored or not normalized; aggregation remains COUNT instead of cardinality
Statistic mapping	No mapping from AggregationOperator::Cardinality → Statistic::Cardinality
Capability matching	Statistic::Cardinality only maps to SetAggregator / DeltaSetAggregator, not HLL
Precompute	Missing HllAccumulator, factory dispatch, and serde support for SketchType::HLL
SQL matcher	SQLPatternMatcher rejects "CARDINALITY" and enforces distinct targets to be value_columns only