feat(parallel): add GIL-free parallel DE with Rust objectives

- Implement RustObjective trait for GIL-free parallelization
- Add 5 benchmark functions: Sphere, Rosenbrock, Rastrigin, Ackley, Griewank
  * Each implements RustObjective with evaluate(), dimension(), global_optimum()
  * Exposed to Python with __call__ method

- Add parallel_differential_evolution_rust() function:
  * Uses Rayon for parallel population evaluation
  * Works with RustObjective implementations only
  * Eliminates Python GIL overhead for 10-100× speedup
  * Supports all DE strategies and adaptive parameters

- Create comprehensive examples:
  * parallel_de_benchmark.py: Performance benchmarks showing speedup
  * polaroid_optimizr_integration.py: 4 workflows combining Polaroid + OptimizR
    - Regime detection with HMM
    - Strategy parameter optimization
    - Portfolio risk analysis
    - Pairs trading pipeline

- Module integration:
  * Export benchmark functions in Python API
  * Export parallel_differential_evolution_rust
  * Update __init__.py and core.py with new functions

- Technical implementation:
  * RustObjective trait in src/rust_objectives.rs
  * Parallel evaluation uses par_iter() from Rayon
  * Per-thread RNG seeding for reproducibility
  * Maintains same API as standard DE for easy comparison

Part of Priority 2: Enable Rust parallelization (Enhancement Strategy)
Expected speedup: 10-100× on multi-core systems for pure Rust objectives

python/optimizr/__init__.py

@@ -13,6 +13,7 @@ from optimizr.hmm import HMM
 from optimizr.core import (
     mcmc_sample,
     differential_evolution,
+    parallel_differential_evolution_rust,
     grid_search,
     mutual_information,
     shannon_entropy,
@@ -30,6 +31,12 @@ from optimizr.core import (
     return_statistics_py,
     create_lagged_features_py,
     rolling_correlation_py,
+    # Benchmark functions
+    Sphere,
+    Rosenbrock,
+    Rastrigin,
+    Ackley,
+    Griewank,
 )
 
 # Try to import maths_toolkit from Rust backend
@@ -44,6 +51,7 @@ __all__ = [
     "HMM",
     "mcmc_sample",
     "differential_evolution",
+    "parallel_differential_evolution_rust",
     "grid_search",
     "mutual_information",
     "shannon_entropy",
@@ -61,5 +69,11 @@ __all__ = [
     "return_statistics_py",
     "create_lagged_features_py",
     "rolling_correlation_py",
+    # Benchmark functions
+    "Sphere",
+    "Rosenbrock",
+    "Rastrigin",
+    "Ackley",
+    "Griewank",
     "maths_toolkit",
 ]

python/optimizr/core.py

@@ -11,6 +11,7 @@ try:
     from optimizr._core import (
         mcmc_sample as _rust_mcmc_sample,
         differential_evolution as _rust_differential_evolution,
+        parallel_differential_evolution_rust,
         grid_search as _rust_grid_search,
         mutual_information as _rust_mutual_information,
         shannon_entropy as _rust_shannon_entropy,
@@ -28,6 +29,12 @@ try:
         return_statistics_py,
         create_lagged_features_py,
         rolling_correlation_py,
+        # Benchmark functions
+        Sphere,
+        Rosenbrock,
+        Rastrigin,
+        Ackley,
+        Griewank,
     )
     RUST_AVAILABLE = True
 except ImportError: