Fix SmartHLL ClassCastException in GROUP BY ORDER BY

[ilamhs]

extractGroupByResult() blindly cast to Set but the holder can contain a HyperLogLog once the dict-ID cardinality threshold is exceeded via checkAndConvertToSketchForGroups. Mirror the threshold check already present in extractAggregationResult().

Labels: bugfix

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.92%. Comparing base (63bf8dc) to head (63e033e).
⚠️ Report is 81 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18841      +/-   ##
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+ Coverage     64.76%   64.92%   +0.15%     
- Complexity     1322     1347      +25     
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  Files          3393     3395       +2     
  Lines        211022   212533    +1511     
  Branches      33135    33515     +380     
============================================
+ Hits         136676   137992    +1316     
- Misses        63330    63389      +59     
- Partials      11016    11152     +136     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-21	64.92% <100.00%> (+0.15%)	⬆️
temurin	64.92% <100.00%> (+0.15%)	⬆️
unittests	64.92% <100.00%> (+0.15%)	⬆️
unittests1	56.95% <100.00%> (-0.03%)	⬇️
unittests2	37.24% <0.00%> (+0.06%)	⬆️

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[Vamsi-klu]

Traced the root cause and the fix looks correct. checkAndConvertToSketchForGroups (called from both aggregateGroupBySV and aggregateGroupByMV) does setValueForKey(groupKey, convertToSketch(dictIdsWrapper)) once a group's dict-id cardinality exceeds getDictIdCardinalityThreshold(), so the group holder can legitimately hold a sketch rather than a DictIdsWrapper. The old return (Set) result cast then CCE'd on it. Widening the return to Object and returning result directly mirrors extractAggregationResult (whose else-branch already returns the raw sketch), and since the non-grouped path already emits sketches, downstream merge/serialization handles the type fine. Good that this sits in the shared base, so it also covers the sibling subclasses (SmartHLLPlus and SmartULL), not just SmartHLL.

One note on the test: it plants a HyperLogLog directly via setValueForKey rather than driving aggregation past the threshold, so it pins the changed line (asserts extracted instanceof HyperLogLog and not a Set) but doesn't exercise checkAndConvertToSketchForGroups end-to-end. It's a valid regression test, but an aggregation-driven case that pushes a group over dictThreshold would guard the whole conversion->extraction path against future regressions.