Adds heuropt-plot, a tiny SVG-only plotter that takes heuropt
results and emits scatter plots (pareto_front_svg) and line plots
(convergence_svg). No heavy 'plotters' or 'tiny-skia' dep — hand-
rolled SVG so the crate adds <100 KB to a build.
Workspace setup: root Cargo.toml gains [workspace] with members =
['.', 'heuropt-plot']. heuropt-plot has its own version (0.1.0) and
publishes independently against heuropt 0.7+.
Adds examples/visualize.rs that wires it all up: NSGA-II on Schaffer
N.1, observer closure recording per-generation hypervolume, two SVGs
written to disk.
swaits
8cf518200a