Add settlement logic for option expiry with Settlement exit reason, leg_expiry_timestamps parameter for per-leg expiry tracking, and new single-leg spread types (LongCall, LongPut, NakedCall, NakedPut). Positions are force-closed at settlement with premiums replaced by intrinsic value, and re-entry is prevented after all legs expire.
Introduces PyBatchSpreadItem and batch_spread_backtest function for running multiple spread strategies in parallel using Rayon, enabling efficient multi-strategy backtesting workflows.
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.
porcelaincode