feat(Function): Add __eq__ method and improve quadratic_solve stability

Implements two features for the Function class:

1.  Adds the `__eq__` operator (`==`) to allow for logical comparison of two Function objects based on their coefficients.
2.  Replaces the standard quadratic formula with a numerically stable version in `quadratic_solve` to prevent "catastrophic cancellation" errors and improve accuracy.

pyproject.toml

@@ -5,7 +5,7 @@ build-backend = "setuptools.build_meta"
 [project]
 # --- Core Metadata ---
 name = "polysolve"
-version = "0.6.1"
+version = "0.6.2"
 authors = [
   { name="Jonathan Rampersad", email="[email protected]" },
 ]