feat(traits): add Repair<D> trait + ClampToBounds and ProjectToSimplex impls

Spec §22 Round 4-D listed bounded mutation / repair operators as future
work; this is the second piece of that. A `Repair<D>` trait that nudges
infeasible decisions back to feasibility, intended to be called from a
user's Variation operator (or a CompositeVariation pipeline) when
projection-style constraint handling is preferred over the
penalty-style `constraint_violation` approach.

Trait:
  pub trait Repair<D> {
      fn repair(&mut self, decision: &mut D);
  }

Provided impls:
- `ClampToBounds` — clamps each variable of a Vec<f64> to per-axis bounds
- `ProjectToSimplex` — projects a Vec<f64> onto the (clipped) probability
  simplex (Σ x_i = total, x_i ≥ 0), useful for portfolio-style problems
  and reference-direction normalization

Both stay in the existing `operators` module (alongside Variation
operators) since they share the same "transforms decisions" theme. Re-
exported from the prelude.

src/prelude.rs

@@ -9,7 +9,7 @@ pub use crate::core::{
     Population, Problem, Rng, rng_from_seed,
 };
 
-pub use crate::traits::{Initializer, Optimizer, Variation};
+pub use crate::traits::{Initializer, Optimizer, Repair, Variation};
 
 pub use crate::pareto::{
     Dominance, ParetoArchive, best_candidate, crowding_distance, das_dennis,
@@ -17,8 +17,9 @@ pub use crate::pareto::{
 };
 
 pub use crate::operators::{
-    BitFlipMutation, BoundedGaussianMutation, CompositeVariation, GaussianMutation,
-    LevyMutation, PolynomialMutation, RealBounds, SimulatedBinaryCrossover, SwapMutation,
+    BitFlipMutation, BoundedGaussianMutation, ClampToBounds, CompositeVariation,
+    GaussianMutation, LevyMutation, PolynomialMutation, ProjectToSimplex, RealBounds,
+    SimulatedBinaryCrossover, SwapMutation,
 };
 
 pub use crate::algorithms::{