chore(batch-processing): add concurrency and stress tests

[hjgraca]

Please provide the issue number

Issue number: #1095

Summary

Changes

• Add BatchProcessingStressTests for high-concurrency and sustained load validation
• Add BatchProcessingThreadSafetyTests to verify thread-safe record processing
• Add isolation tests for DynamoDB, Kinesis, SQS, and typed batch processors
• Add StaticResultPropertyTests to validate static result property behavior
• Add helper classes for concurrent invocation results, test event factory, and record handlers
• Add project reference to BatchProcessing library in test project
• Verify batch processor maintains correctness under high concurrency (20-100 concurrent invocations)
• Validate thread safety with concurrent record processing and state isolation
• Ensure no record leakage between concurrent invocations
• Test stress scenarios with varying concurrency levels and iteration counts

User experience

Please share what the user experience looks like before and after this change

Checklist

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• Meets tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.50%. Comparing base (eb7ba1d) to head (a3fe222).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1096      +/-   ##
===========================================
- Coverage    78.56%   78.50%   -0.07%     
===========================================
  Files          299      299              
  Lines        12375    12375              
  Branches      1492     1492              
===========================================
- Hits          9723     9715       -8     
- Misses        2178     2186       +8     
  Partials       474      474              

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