feat(ga): Implement quality filtering and precision-based clustering (#19)

The previous GA logic was returning the "top N" solutions, which led to test failures when the algorithm correctly converged on only one of all possible roots (e.g., returning 1000 variations of -1.0).

This commit fixes the root-finding logic to correctly identify and return *all* unique, high-quality roots:

1.  **feat(api):** Adds `root_precision` to `GA_Options`. This new parameter (default: 5) allows the user to control the number of decimal places for clustering unique roots.

2.  **fix(ga):** Replaces the flawed "top N" logic in both `_solve_x_numpy` and `_solve_x_cuda`. The new process is:
    * Dynamically sets a `quality_threshold` based on the user's `root_precision` (e.g., `precision=5` requires a rank > `1e6`).
    * Filters the *entire* final population for all solutions that meet this quality threshold.
    * Rounds these high-quality solutions to `root_precision`.
    * Returns only the `np.unique()` results.

This ensures the solver returns all distinct roots that meet the accuracy requirements, rather than just the top N variations of a single root.

Reviewed-on: #19
Co-authored-by: Jonathan Rampersad <rampersad.jonathan@gmail.com>
Co-committed-by: Jonathan Rampersad <rampersad.jonathan@gmail.com>

pyproject.toml

@@ -5,7 +5,7 @@ build-backend = "setuptools.build_meta"
 [project]
 # --- Core Metadata ---
 name = "polysolve"
-version = "0.4.2"
+version = "0.5.0"
 authors = [
   { name="Jonathan Rampersad", email="jonathan@jono-rams.work" },
 ]