Support GROUP BY GROUPING SETS / ROLLUP / CUBE in the multi-stage query engine

[xiangfu0]

Summary

Adds native execution of GROUP BY GROUPING SETS (...) / ROLLUP(...) / CUBE(...) and the
GROUPING() / GROUPING_ID() functions to the multi-stage query engine (MSE), building on the
single-stage support in #18662.

Two execution paths, both producing identical results:

• Aggregate directly over a table scan — the whole aggregate is pushed down to the single-stage (leaf)
  engine, which expands each row across the grouping sets and appends the synthetic $groupingId discriminator.
  Reuses the single-stage engine wholesale (the Doris/StarRocks backend-expansion model).
• Aggregate over any other input (e.g. after a JOIN) — a new RepeatOperator in the multi-stage runtime
  performs the same per-set row expansion (NULLing rolled-up columns, appending $groupingId), then an ordinary
  GROUP BY over [union keys…, $groupingId] runs — no grouping-set-specific aggregation logic.

Plan split (PinotAggregateExchangeNodeInsertRule): LEAF → EXCHANGE(hash union+$groupingId) → FINAL(group by union+$groupingId) → PROJECT. The PROJECT computes GROUPING() / GROUPING_ID() from
$groupingId (bit extraction), mirroring the single-stage post-aggregation handler, and drops $groupingId.
GROUPING / GROUPING_ID are registered in PinotOperatorTable, and explicit
GROUP BY GROUPING SETS ((a, b), …) tuple syntax is accepted by the validator.

Tests

GroupingSetsQueriesTest — grouping-set aggregation, GROUPING() / GROUPING_ID() (SELECT and HAVING),
filtered aggregation, composite/nested sets, explicit GROUPING SETS syntax, and grouping sets over a JOIN —
run against both engines (the order-independent cases via the useBothQueryEngines data provider), plus the
single-stage genuine-vs-rolled-up-NULL discrimination cases. All green.

Known limitations (rejected with a clear error → never wrong results)

• The v2 physical planner (usePhysicalOptimizer=true, opt-in, default off) still rejects grouping sets; the
  default planner is fully supported. (Follow-up.)
• More than 31 distinct grouping columns (the $groupingId bitmask is a 32-bit int) — same cap as the
  single-stage engine.
• Leaf group-trim (ORDER BY … LIMIT pushdown) is not pushed for grouping-set queries; results are still correct
  (the broker applies the final ORDER BY + LIMIT).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.83805% with 129 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.82%. Comparing base (9ceca0f) to head (ffaebbf).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
...r/physical/v2/opt/rules/AggregatePushdownRule.java	9.37%	56 Missing and 2 partials ⚠️
...he/pinot/query/runtime/plan/PlanNodeToOpChain.java	0.00%	28 Missing and 1 partial ⚠️
...org/apache/pinot/core/data/table/TableResizer.java	12.50%	7 Missing ⚠️
...inot/core/query/reduce/PostAggregationHandler.java	12.50%	7 Missing ⚠️
...e/pinot/query/runtime/operator/RepeatOperator.java	89.47%	6 Missing ⚠️
...egation/groupby/GroupingSetsGroupKeyGenerator.java	0.00%	4 Missing ⚠️
...el/rules/PinotAggregateExchangeNodeInsertRule.java	93.18%	0 Missing and 3 partials ⚠️
...y/planner/physical/v2/nodes/PhysicalAggregate.java	40.00%	1 Missing and 2 partials ⚠️
...not/query/runtime/operator/MultiStageOperator.java	25.00%	3 Missing ⚠️
...org/apache/pinot/sql/parsers/CalciteSqlParser.java	93.54%	0 Missing and 2 partials ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             master   #18817    +/-   ##
==========================================
  Coverage     64.81%   64.82%            
  Complexity     1347     1347            
==========================================
  Files          3396     3398     +2     
  Lines        212503   212803   +300     
  Branches      33484    33534    +50     
==========================================
+ Hits         137732   137943   +211     
- Misses        63610    63679    +69     
- Partials      11161    11181    +20     

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	64.82% <66.83%> (+<0.01%)	⬆️
temurin	64.82% <66.83%> (+<0.01%)	⬆️
unittests	64.81% <66.83%> (+<0.01%)	⬆️
unittests1	56.81% <66.83%> (+0.02%)	⬆️
unittests2	37.17% <5.91%> (-0.06%)	⬇️

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[xiangfu0]

Found one high-signal compatibility issue; see inline comment.

[xiangfu0]

Found one high-signal issue in the new v2 grouping-sets path; see inline comment.

[gortiz]

Nice contribution!