Move aggregate and shuffle stats to the columnar module

[gerashegalov]

Related to #14834.

Description

This PR is one reviewable layer in the unshim stack introduced by #15025. It moves aggregate and shuffle stat value classes into the columnar helper module, completing the focused statistics-helper movement before caller updates.

Stack context

• Stack introduction: Add default common unshim packaging flow #15025
• Previous layer: Move profile and write stats to the columnar module #15046
• Next layer: Adapt rule and plugin metadata callers to Java helpers #15048

Testing and validation notes

• No standalone behavior change is intended in this layer. It is covered by the full-stack packaging/build validation described in Add default common unshim packaging flow #15025 and the existing tests for the affected subsystem.
• The full split stack was verified to be tree-equivalent to the pre-split stack top.

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
  (Covered by the validation notes in the PR description.)
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required

[greptile-apps]

Greptile Summary

This is an intermediate layer in a stacked refactor that migrates aggregate and shuffle statistics value classes from Scala case classes in sql-plugin into Java classes in the new sql-plugin-columnar module. No logic changes are intended.

• Eight new Java value classes are added to sql-plugin-columnar covering aggregate mode info, async/throttling metrics, shuffle block/transaction types, and join options/cardinality stats — all porting the Scala originals faithfully with matching validation messages and floating-point comparison via Double.compare.
• WindowedBlockIteratorSuite is updated from the Scala companion-object call style (BlockRange(...)) to explicit constructor syntax (new BlockRange(...)) so the tests compile correctly once the Scala case class is removed in a subsequent stack layer.
• BlockRange and BlockWithSize temporarily exist in both sql-plugin (Scala) and sql-plugin-columnar (Java) under the same package; this intermediate state is intentional and resolves when the originals are deleted in the next layer.

Confidence Score: 4/5

Safe to merge as part of the full stack; the Java value classes are faithful ports with no behavioral change.

All eight new Java classes are straightforward read-only value types with no GPU memory allocation, no concurrency changes, and no altered business logic. The only noteworthy inconsistency is that JoinCardinalityStats and JoinOptions declare serialVersionUID = 0L while the five other new Serializable classes in the same PR use 1L; this does not affect correctness at runtime but could cause silent InvalidClassException failures in an unlikely rolling-upgrade scenario.

JoinCardinalityStats.java and JoinOptions.java — the serialVersionUID = 0L choice differs from peer classes and is worth confirming as intentional before the Scala originals are removed.

Important Files Changed

Filename	Overview
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/AggregateModeInfo.java	New Java value class for aggregate mode info, ported from Scala case class; all fields private final with correct equals/hashCode/toString.
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/io/async/AsyncMetrics.java	New Java value class for async task scheduling/execution timings; immutable, Serializable, correct equals/hashCode.
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/io/async/ThrottlingExecutorStats.java	New Java mutable stats class matching the original Scala case class with var fields; public mutable fields are intentional to allow in-place accumulation by ThrottlingExecutor.
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/shuffle/BlockRange.java	Java port of the Scala case class BlockRange; preserves validation logic and error message ("requirement failed:") from the Scala original.
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/shuffle/BlockWithSize.java	New Java interface corresponding to the Scala trait BlockWithSize; minimal and correct.
sql-plugin-columnar/src/main/java/com/nvidia/spark/rapids/shuffle/TransactionStats.java	New Java value class for shuffle transaction stats; correctly uses Double.compare for floating-point equality; not Serializable (consistent with its local-logging purpose).
sql-plugin-columnar/src/main/java/org/apache/spark/sql/rapids/execution/JoinCardinalityStats.java	New Java port of JoinCardinalityStats; leftNullCounts and rightNullCounts use Seq<?> (required due to Scala Long erasure), losing the Seq[Long] type contract; serialVersionUID is 0L inconsistently with peer classes.
sql-plugin-columnar/src/main/java/org/apache/spark/sql/rapids/execution/JoinOptions.java	New Java port of JoinOptions; serialVersionUID is 0L inconsistently with peer classes; otherwise correct.
tests/src/test/scala/com/nvidia/spark/rapids/shuffle/WindowedBlockIteratorSuite.scala	Test updated to use new BlockRange(…) constructor syntax instead of Scala companion-object apply; semantically equivalent and forward-compatible with the Java class replacement.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    subgraph sql-plugin-columnar [sql-plugin-columnar NEW Java classes]
        AM[AggregateModeInfo]
        AMX[AsyncMetrics]
        TE[ThrottlingExecutorStats]
        BR[BlockRange]
        BW[BlockWithSize]
        TS[TransactionStats]
        JC[JoinCardinalityStats]
        JO[JoinOptions]
        BW --> BR
    end

    subgraph sql-plugin [sql-plugin Scala originals - removed in later layer]
        AM2[AggregateModeInfo case class]
        TE2[ThrottlingExecutorStats case class]
        BR2[BlockRange case class]
        BW2[BlockWithSize trait]
        JC2[JoinCardinalityStats case class]
        JO2[JoinOptions case class]
        WBI[WindowedBlockIterator]
        BW2 --> BR2
        BR2 --> WBI
    end

    subgraph tests
        WBIS[WindowedBlockIteratorSuite\nnew BlockRange - updated syntax]
    end

    sql-plugin-columnar --> sql-plugin
    sql-plugin --> tests

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