0ff67e7fe2
Add two new risk/reward metrics to BacktestMetrics: - payoff_ratio: avg winning return / avg losing return (absolute) - recovery_factor: net profit / max drawdown in absolute terms Computed in both StreamingMetrics::finalize() and PortfolioEngine. Exposed via PyO3 with #[pyo3(get)] on PyBacktestMetrics. Updated README with API reference and changelog.