chore: silence clippy warnings

- 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.

src/pareto/crowding.rs

@@ -33,6 +33,7 @@ pub fn crowding_distance<D>(
         .map(|&idx| objectives.as_minimization(&population[idx].evaluation.objectives))
         .collect();
 
+    #[allow(clippy::needless_range_loop)] // `k` indexes into nested vectors below.
     for k in 0..m {
         // Sort indices into `front` by objective k.
         let mut order: Vec<usize> = (0..n).collect();