feat: drop heuropt-plot companion crate

Removes the heuropt-plot subcrate, the visualize example that used
it, and the related workspace plumbing (root [workspace] table, the
[workspace] override added to fuzz/Cargo.toml to detach from it,
heuropt-plot dev-dep, CHANGELOG mention).

The visualization concern is better served as an independent third-
party project than as a companion crate in this repo. No effect on
heuropt's public API or the async work in 0.8.0.

examples/visualize.rs

@@ -1,53 +0,0 @@
-//! Visualize an NSGA-II run on Schaffer N.1 with the `heuropt-plot`
-//! companion crate — produces a `pareto_front.svg` of the final
-//! Pareto front.
-//!
-//! Run with: `cargo run --release --example visualize`
-
-use heuropt::prelude::*;
-use heuropt_plot::pareto_front_svg;
-
-struct Schaffer;
-
-impl Problem for Schaffer {
-    type Decision = Vec<f64>;
-    fn objectives(&self) -> ObjectiveSpace {
-        ObjectiveSpace::new(vec![Objective::minimize("f1"), Objective::minimize("f2")])
-    }
-    fn evaluate(&self, x: &Vec<f64>) -> Evaluation {
-        Evaluation::new(vec![x[0] * x[0], (x[0] - 2.0).powi(2)])
-    }
-}
-
-fn main() {
-    let problem = Schaffer;
-    let bounds = vec![(-5.0_f64, 5.0_f64)];
-    let space = problem.objectives();
-
-    let mut opt = Nsga2::new(
-        Nsga2Config {
-            population_size: 50,
-            generations: 100,
-            seed: 42,
-        },
-        RealBounds::new(bounds.clone()),
-        CompositeVariation {
-            crossover: SimulatedBinaryCrossover::new(bounds.clone(), 15.0, 0.5),
-            mutation: PolynomialMutation::new(bounds, 20.0, 1.0),
-        },
-    );
-
-    let result = opt.run(&problem);
-
-    let svg = pareto_front_svg(
-        &result.pareto_front,
-        &space,
-        700,
-        450,
-        "NSGA-II on Schaffer N.1 — final Pareto front",
-    );
-    std::fs::write("pareto_front.svg", svg).expect("write pareto_front.svg");
-
-    println!("Final front size: {}", result.pareto_front.len());
-    println!("Wrote pareto_front.svg");
-}