feat: Add comprehensive regression analysis engine

- Implement RegressionAnalyzer with three baseline strategies (FixedBaseline, RollingAverage, PreviousRun)
- Add PerformanceTrend enum and statistical significance testing with configurable thresholds
- Create OperationAnalysis and RegressionReport structures for detailed analysis results
- Add comprehensive accessor methods to TimestampedResults and HistoricalResults
- Refactor PerformanceReport to use enhanced RegressionAnalyzer instead of simple comparison
- Provide extensive test coverage for all regression analysis strategies and edge cases

Author: Wandalen