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/operators/binary.rs

@@ -45,7 +45,7 @@ mod tests {
         let mut m = BitFlipMutation { probability: 0.0 };
         let mut rng = rng_from_seed(0);
         let parent = vec![false, true, false, true, true];
-        let children = m.vary(&[parent.clone()], &mut rng);
+        let children = m.vary(std::slice::from_ref(&parent), &mut rng);
         assert_eq!(children.len(), 1);
         assert_eq!(children[0], parent);
     }
@@ -55,7 +55,7 @@ mod tests {
         let mut m = BitFlipMutation { probability: 1.0 };
         let mut rng = rng_from_seed(0);
         let parent = vec![false, true, false, true, true];
-        let children = m.vary(&[parent.clone()], &mut rng);
+        let children = m.vary(std::slice::from_ref(&parent), &mut rng);
         let expected: Vec<bool> = parent.iter().map(|b| !b).collect();
         assert_eq!(children[0], expected);
     }

src/operators/permutation.rs

@@ -46,7 +46,7 @@ mod tests {
         let mut m = SwapMutation;
         let mut rng = rng_from_seed(11);
         let parent = vec![0_usize, 1, 2, 3, 4];
-        let children = m.vary(&[parent.clone()], &mut rng);
+        let children = m.vary(std::slice::from_ref(&parent), &mut rng);
         assert_eq!(children.len(), 1);
         assert_eq!(sorted(children[0].clone()), sorted(parent));
     }
@@ -56,7 +56,7 @@ mod tests {
         let mut m = SwapMutation;
         let mut rng = rng_from_seed(0);
         let parent = vec![42_usize];
-        let children = m.vary(&[parent.clone()], &mut rng);
+        let children = m.vary(std::slice::from_ref(&parent), &mut rng);
         assert_eq!(children[0], parent);
     }
 
@@ -65,7 +65,7 @@ mod tests {
         let mut m = SwapMutation;
         let mut rng = rng_from_seed(0);
         let parent = vec![1_usize, 2];
-        let children = m.vary(&[parent.clone()], &mut rng);
+        let children = m.vary(std::slice::from_ref(&parent), &mut rng);
         assert_eq!(children[0], vec![2, 1]);
     }
 }

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();