feat(ga): Overhaul GA for multi-root robustness and CPU performance

### 🚀 Performance (CPU)
* Replaces `np.polyval` with a parallel Numba JIT function (`_calculate_ranks_numba`).
* Replaces $O(N \log N)$ `np.argsort` with $O(N)$ `np.argpartition` in the GA loop.
* Adds `numba` as a core dependency.

### 🧠 Robustness (Algorithm)
* Implements Blend Crossover (BLX-$\alpha$) for better, extrapolative exploration.
* Uses a hybrid selection model (top X% for crossover, 100% for mutation) to preserve root niches.
* Adds `selection_percentile` and `blend_alpha` to `GA_Options` for tuning.

pyproject.toml

@@ -5,7 +5,7 @@ build-backend = "setuptools.build_meta"
 [project]
 # --- Core Metadata ---
 name = "polysolve"
-version = "0.5.1"
+version = "0.6.0"
 authors = [
   { name="Jonathan Rampersad", email="jonathan@jono-rams.work" },
 ]
@@ -33,7 +33,8 @@ classifiers = [
 
 # --- Dependencies ---
 dependencies = [
-    "numpy>=1.21"
+    "numpy>=1.21",
+    "numba"
 ]
 
 # --- Optional Dependencies (Extras) ---