feat: implement comprehensive performance testing framework

[berntpopp]

Summary

Implement comprehensive performance testing framework in tests/performance/ to systematically measure pipeline performance and detect regressions.

Current State

• Basic benchmarking exists (benchmark_pipeline.py)
• No automated regression detection
• Missing stage-specific performance tests

Proposed Implementation

tests/performance/
├── test_memory_profiling.py
├── test_cpu_utilization.py  
├── test_scalability.py
├── test_regression_detection.py
├── stage_benchmarks/
│   ├── test_setup_stages.py
│   ├── test_processing_stages.py
│   ├── test_analysis_stages.py
│   └── test_output_stages.py
└── integration/
    ├── test_pipeline_performance.py
    └── test_feature_performance.py

Tasks

• Memory and CPU profiling utilities
• Individual stage performance tests
• Automated regression detection
• CI/CD integration with performance gates
• Performance reporting dashboard

Success Criteria

• All performance tests pass in CI
• Performance baselines established
• Automated regression detection active
• Performance improvements validated