Decouple PPL logical plans from UDT temporal types

[penghuo]

Description

This PR makes two related but distinct architectural changes to the Calcite-side PPL planner. Together they let logical RelNode/RexNode trees produced during analysis use ordinary Calcite types end-to-end. UDTs (and ExprType) only re-enter the picture immediately before physical execution, where they're needed to keep Linq4j codegen seeing the existing VARCHAR-backed runtime representation.

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1. Decouple ExprType from the logical plan

Calcite-side PPL planning code (RelNode/RexNode construction, coercion, type checking, UDF return-type inference, UDF implementors) now operates on RelDataType directly instead of converting to/from ExprType at every step.

• Coercion (CoercionUtils): new RelDataType-typed common-type resolver with an internal widening DAG keyed by a small CoercionTag enum (matches v2 widening semantics — STRING → TIMESTAMP direct edge, UNDEFINED → any-concrete unit cost, etc).
• Type checking (PPLTypeChecker): signatures expressed as List<List<RelDataType>>; new renderTypeName for error messages; new temporalKind helper that canonicalizes DATE/TIME/TIMESTAMP across UDT and standard SQL temporal forms in a single place.
• Operand metadata (PPLOperandTypes, UDFOperandMetadata): signature constants exposed as RelDataType (e.g. INTEGER_T, STRING_T, IP_UDT).
• UDF implementors (AddSubDate, Extract, Format, LastDay, PeriodName, TimestampAdd, TimestampDiff, Weekday, Span, WidthBucket, IPFunction, CidrMatchFunction, CompareIpFunction, geo-IP, CurrentFunction): branch on RelDataType (UDT class instances or SqlTypeName) and pass RelDataType through their lowering, instead of bouncing through ExprType.
• CalciteRexNodeVisitor.visitCast: maps AST DataType directly to RelDataType, removing the DataType.getCoreType() round-trip.
• ExtendedRexBuilder: type discrimination via instanceof UDT classes and SqlTypeName, no ExprType conversion.

UDT identity is preserved at planning time via instanceof checks (not getExprType()); subclasses survive createTypeWithNullability / createTypeWithCharsetAndCollation via a cloneWith hook on ExprSqlType/ExprJavaType.

2. Remove DATE/TIME/TIMESTAMP UDTs from the logical plan

After the ExprType decoupling lands, the only thing pinning UDT temporal types to the logical layer was convertExprTypeToRelDataType. This change pushes those UDTs out of the logical plan entirely:

• Type factory: OpenSearchTypeFactory.convertExprTypeToRelDataType returns standard DATE/TIME(9)/TIMESTAMP(9) for the corresponding ExprCoreType. New isStandardTemporalType helper. IP and BINARY remain UDT.
• Cast emission (CalciteRexNodeVisitor.visitCast): emits standard temporal types for AST DATE/TIME/TIMESTAMP cast targets.
• Cast lowering (ExtendedRexBuilder.makeCast): standard temporal targets dispatch to PPLBuiltinOperators.DATE/TIME/TIMESTAMP UDFs but keep the call's RelDataType standard. IP routed separately.
• Pushdown (PredicateAnalyzer): isTimestamp/isDate accept both standard SqlTypeName and UDT, and read literal values via getValueAs(String.class) so TimestampString/DateString round-trip without ClassCastException.
• Constant rename: NULLABLE_*_UDT → NULLABLE_*_T, DATE_UDT/TIME_UDT/TIMESTAMP_UDT → DATE_T/TIME_T/TIMESTAMP_T.
• DatetimeExtension / DatetimeUdtNormalizeRule removed (introduced in Normalize datetime types for unified query API #5408). Their sole purpose was to rewrite UDT temporal return types to standard Calcite types as a unified-API post-analysis pass; the analysis pipeline no longer produces temporal UDTs in the first place, so the rule is a no-op and the extension is removed along with its registrations in UnifiedPplSpec/UnifiedSqlSpec.

TemporalUdtRewriteShuttle (the conversion boundary)

A new RelShuttle runs once at the prepare-statement boundary (OpenSearchCalcitePreparingStmt.implement and OpenSearchRelRunners.run) and rewrites every standard temporal type in the tree back to its UDT counterpart. Implementation notes:

• Atomic rebuild for stateful nodes. Calcite's default RelShuttleImpl.visitChild rebuilds parents via parent.copy(traits, newInputs) after visiting each child, which makes both rewrite-then-visit and visit-then-rewrite orderings briefly violate row-type consistency. The shuttle intercepts Project/Filter/Calc/Aggregate/Values and rebuilds them in one shot with rewritten inputs and rewritten RexNodes together.
• Filter rebuild preserves variablesSet. Without this, correlated subqueries lose their CorrelationId binding.
• RexShuttle extensions: visitSubQuery recurses into the inner plan (Calcite's default doesn't); visitLambda/visitLambdaRef rebuild the lambda body and parameter refs together so transform(arr, x -> ...) over temporal-element arrays stays consistent.
• rewriteType recurses into ARRAY/MULTISET/MAP/struct, so collection-typed temporal columns (e.g. TAKE(@timestamp, 2)) get rewritten.
• TemporalSchemaRewritable marker interface. AbstractCalciteIndexScan implements it and rewrites its schema in place via buildScan(...), rather than wrapping in a LogicalProject(CAST(...)). This is what keeps Linq4j codegen reading String values consistent with what OpenSearchExprValueFactory delivers at runtime.

Other adjustments

• Calcite IT golden files (explain_appendpipe_command.json × 2 profiles): logical plans now show TIMESTAMP(9) instead of EXPR_TIMESTAMP VARCHAR; physical plans still show UDT post-shuttle.

Tests

• New unit tests: TemporalUdtRewriteShuttleTest, CalcitePPLLogicalPlanStandardTemporalTest (proves no temporal UDT appears anywhere in the logical RelNode / RexNode tree for representative queries — table scan, eval-cast, filter, group-by, UDF call), expanded CoercionUtilsTest, expanded OpenSearchTypeFactoryTest.
• All module unit tests pass.
• Full Calcite IT suite (*Calcite*IT) passes: 4968 tests, 0 failures, 0 errors.

Related Issues

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• New PPL command checklist all confirmed.
• API changes companion pull request created.
• Commits are signed per the DCO using `--signoff` or `-s`.
• Public documentation issue/PR created.

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