Add schema-bound polymorphic aggregation across query engines

[xiangfu0]

Polymorphic aggregates currently rely on fixed result types, explicit SQL type arguments, or types discovered from data blocks. This makes empty responses unreliable and can lose logical BOOLEAN/TIMESTAMP types between planning, execution, and reduction.

This change resolves argument and result types once from the input schema and carries an immutable binding through SSE requests and MSE plans. Aggregation providers are discovered through ServiceLoader, so another declared polymorphic aggregate can supply its type rule and implementation without adding factory, planner-stage, or reducer switch branches.

• Support inferred two-argument FIRST_WITH_TIME/LAST_WITH_TIME and one-argument ARRAY_AGG, with an optional boolean distinct argument.
• Preserve logical types for nonnumeric MODE, ANY_VALUE, and the existing SSE EXPR_MIN/EXPR_MAX rewrite.
• Keep bindings through expression overrides, gapfill, grouping, post-aggregation, broker-pruned responses, and LIMIT 0. Read older physical segment types through the bound type's conversion getters.
• Preserve null projections and all tied rows in serialized ExprMin/Max merges; add the extension guide in pinot-core/README.md.

Existing explicit-type FIRST/LAST and ARRAY_AGG forms remain supported. Numeric MODE keeps its DOUBLE result and AVG tie reducer; fixed numeric aggregate contracts are unchanged. Existing calls retain legacy execution when a native transform has no schema-only type rule; the new inferred overloads require resolvable input metadata. Binding fields are optional, but the new inferred overloads and logical-type semantics require upgraded brokers and execution workers. Public ExprMin/Max execution remains SSE-only through its existing configured rewrite.

Validation: 577 focused tests across 39 classes passed in the final reactor run, including both planners, all three MSE fixture execution modes, raw/dictionary segments, distributed merges, null/empty results, and broker-only responses. Spotless, Checkstyle, and license checks passed on all six affected modules. Compilation with warnings enabled used JDK 25 and a local classpath workaround for the missing JetBrains annotation dependency in unchanged compression code; no project dependency was changed. CI and maintainer review are pending.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.78725% with 205 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.88%. Comparing base (6aaa040) to head (cddb856).
⚠️ Report is 22 commits behind head on master.

Files with missing lines	Patch %	Lines
...core/query/aggregation/ExpressionTypeResolver.java	69.59%	19 Missing and 26 partials ⚠️
...che/pinot/segment/spi/AggregationFunctionType.java	63.01%	5 Missing and 22 partials ⚠️
...mmon/function/AggregationFunctionTypeResolver.java	76.27%	8 Missing and 6 partials ⚠️
.../aggregation/GapfillAggregationFunctionBinder.java	87.34%	3 Missing and 7 partials ⚠️
...sthandler/BaseSingleStageBrokerRequestHandler.java	57.14%	7 Missing and 2 partials ⚠️
.../aggregation/function/ModeAggregationFunction.java	92.80%	2 Missing and 7 partials ⚠️
...ation/function/array/ArrayAggFunctionProvider.java	82.97%	2 Missing and 6 partials ⚠️
...apache/pinot/calcite/rel/rules/PinotRuleUtils.java	68.18%	4 Missing and 3 partials ⚠️
...inot/query/planner/logical/RexExpressionUtils.java	33.33%	6 Missing ⚠️
...t/common/request/context/AggregateCallBinding.java	72.22%	2 Missing and 3 partials ⚠️
... and 28 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #19523      +/-   ##
============================================
+ Coverage     67.72%   67.88%   +0.15%     
  Complexity     1430     1430              
============================================
  Files          3489     3499      +10     
  Lines        224634   225772    +1138     
  Branches      35468    35747     +279     
============================================
+ Hits         152130   153256    +1126     
+ Misses        60485    60408      -77     
- Partials      12019    12108      +89     

Flag	Coverage Δ
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-25	67.88% <80.78%> (+0.15%)	⬆️
lane-a	100.00% <ø> (ø)
lane-b	0.00% <ø> (ø)
temurin	67.88% <80.78%> (+0.15%)	⬆️
unittests	67.87% <80.78%> (+0.15%)	⬆️
unittests1	58.14% <80.91%> (+0.36%)	⬆️
unittests2	39.54% <26.42%> (+0.09%)	⬆️

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