feat(timeseries): add time-series integration helpers for financial analysis

- Implement 6 helper functions in src/timeseries_utils.rs:
  * prepare_for_hmm: Feature engineering for HMM regime detection
  * rolling_hurst_exponent: Mean-reversion detection (H < 0.5 = mean-reverting)
  * rolling_half_life: Mean-reversion speed for pairs trading
  * return_statistics: Risk metrics (mean, std, skew, kurt, sharpe)
  * create_lagged_features: ML feature matrix creation
  * rolling_correlation: Rolling correlation for pairs trading

- Add PyO3 bindings in src/timeseries_utils/python_bindings.rs:
  * All functions exposed with _py suffix
  * Proper signature decorators and error handling
  * Registered in lib.rs module system

- Update Python module exports:
  * python/optimizr/core.py: Import from _core
  * python/optimizr/__init__.py: Re-export all functions

- Create comprehensive example:
  * examples/timeseries_integration.py demonstrates all 6 functions
  * Includes integrated pairs trading workflow
  * Shows feature engineering for regime detection

- Technical details:
  * Fixed Array1<f64> type conversions for ndarray compatibility
  * Uses risk_metrics::hurst_exponent and estimate_half_life
  * Built successfully with maturin develop --release (40.93s)
  * All functions tested and working correctly

Part of Priority 3: Time-series integration helpers (Enhancement Strategy)
Addresses v0.3.0 roadmap: Bridge optimization with time-series analysis

src/lib.rs

@@ -33,6 +33,7 @@ use pyo3::types::PyModule;
 pub mod core;
 pub mod functional;
 pub mod maths_toolkit; // Mathematical utilities
+pub mod timeseries_utils; // Time-series integration helpers
 
 // Modular structure (trait-based, generic)
 pub mod de;
@@ -98,5 +99,8 @@ fn _core(_py: Python, m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(risk_metrics::estimate_half_life_py, m)?)?;
     m.add_function(wrap_pyfunction!(risk_metrics::bootstrap_returns_py, m)?)?;
 
+    // Time-series utility functions
+    timeseries_utils::python_bindings::register_python_functions(m)?;
+
     Ok(())
 }