Fix LeafOperator thread accountant

[Jackie-Jiang]

Summary

This PR fixes the thread accountant setup in LeafOperator to properly handle resource accounting for multi-stage query execution.

Changes

• Changed from setupWorker() to setupRunner() for thread accountant initialization
• Added proper cleanup with Tracing.ThreadAccountantOps.clear() in finally blocks
• Treats LeafOperator threads as SSE runner anchor threads instead of worker threads
• Ensures consistent thread accounting for both single table and dual table scenarios

Technical Details

The fix addresses thread accounting issues by:

1. Using setupRunner with queryId and workloadName instead of setupWorker with taskId
2. Adding proper resource cleanup in finally blocks to prevent resource leaks
3. Ensuring consistent behavior between single-request and multi-request execution paths

Files Changed

• pinot-query-runtime/src/main/java/org/apache/pinot/query/runtime/operator/LeafOperator.java

Testing

• Code compiles successfully
• Existing tests pass
• Manual testing of multi-stage queries

This change improves resource management and prevents potential memory/thread accounting issues in multi-stage query execution.

[Copilot]

Pull Request Overview

This PR fixes thread accounting issues in the LeafOperator by changing how thread accountants are initialized and cleaned up for multi-stage query execution. The fix ensures proper resource management by treating LeafOperator threads as SSE runner anchor threads instead of worker threads.

Key changes:

• Replace setupWorker() calls with setupRunner() for proper thread accountant initialization
• Add cleanup calls with Tracing.ThreadAccountantOps.clear() in finally blocks
• Ensure consistent thread accounting behavior for both single and dual table execution scenarios

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 42.85714% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.31%. Comparing base (5799642) to head (2001f84).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
...che/pinot/query/runtime/operator/LeafOperator.java	42.85%	16 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #16651      +/-   ##
============================================
+ Coverage     63.29%   63.31%   +0.02%     
  Complexity     1379     1379              
============================================
  Files          3033     3033              
  Lines        176632   176649      +17     
  Branches      27113    27113              
============================================
+ Hits         111796   111843      +47     
+ Misses        56241    56230      -11     
+ Partials       8595     8576      -19     

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-11	63.27% <42.85%> (+0.02%)	⬆️
java-21	63.26% <42.85%> (+<0.01%)	⬆️
temurin	63.31% <42.85%> (+0.02%)	⬆️
unittests	63.31% <42.85%> (+0.02%)	⬆️
unittests1	56.44% <42.85%> (+0.04%)	⬆️
unittests2	33.11% <0.00%> (-0.01%)	⬇️

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