Completes the rustdoc audit — every public item now has at least one
```rust example block in its docstring, exercised by
`cargo test --doc` (55 doctests, all passing).
- Operators: BitFlipMutation, SwapMutation, RealBounds,
GaussianMutation, BoundedGaussianMutation,
SimulatedBinaryCrossover, PolynomialMutation, LevyMutation,
ClampToBounds, ProjectToSimplex.
- Metrics: hypervolume_2d, hypervolume_nd, spacing.
- Pareto utilities: pareto_compare, pareto_front, best_candidate,
non_dominated_sort, crowding_distance, das_dennis,
ParetoArchive.
Each example is short (5-15 lines) and self-contained — copy-paste
into a fresh project and it runs.
- pareto/crowding.rs: rewrite the inner loop to iterate per-objective
via index_axis-style indexing on `oriented` rather than naming an
unused loop variable `k`.
- operators/{binary,permutation}.rs tests: pass parents via
`std::slice::from_ref` instead of `&[parent.clone()]` to avoid the
cloned_ref_to_slice_refs lint.
Pure cleanup — no behavior change, all 83 unit tests + 2 doctests still
pass.
Variation that clones the first parent and flips each bit independently
with probability `probability`. Panics if probability is outside [0, 1]
(spec §11.3).
Tests verify that probability=0 produces an unchanged child and
probability=1 flips every bit (spec §18.3).
swaits