feat(operators): add BoundedGaussianMutation

A bounded variant of GaussianMutation: same Gaussian noise applied to
the first parent, but every variable is clamped to its per-dimension
inclusive bound. Useful as a drop-in for problems that need feasibility
maintained across generations rather than relying on
clamp-inside-evaluate.

Panics on `sigma <= 0.0`, on no parents, and on construction if any
`(lo, hi)` has `lo > hi`. Decision length must match the bounds
length when called.

src/prelude.rs

@@ -16,7 +16,9 @@ pub use crate::pareto::{
     pareto_compare, pareto_front,
 };
 
-pub use crate::operators::{BitFlipMutation, GaussianMutation, RealBounds, SwapMutation};
+pub use crate::operators::{
+    BitFlipMutation, BoundedGaussianMutation, GaussianMutation, RealBounds, SwapMutation,
+};
 
 pub use crate::algorithms::{
     DifferentialEvolution, DifferentialEvolutionConfig, Nsga2, Nsga2Config, Paes, PaesConfig,