feat(algorithms): add PesaII (Pareto Envelope-based Selection Algorithm II)

Corne, Jerram, Knowles & Oates 2001: divides objective space into a
hyperbox grid and uses per-box population counts to drive selection
toward sparsely-populated regions.

Each generation:
- Maintain an external archive of non-dominated members
- Build a hyperbox grid (`grid_divisions` per axis on the archive's
  current axis ranges); count members per box
- Selection picks two parents by region-based tournament: choose two
  random non-empty boxes and take a uniform-random member from the
  one with fewer occupants
- Variation produces an offspring; insert into archive, dropping
  dominated members and (if archive overflows) the most-crowded
  occupant of the most-occupied box

Tests cover non-empty front on Schaffer N.1, deterministic reruns,
and panic on `archive_size == 0`.

src/algorithms/sms_emoa.rs

@@ -8,7 +8,7 @@ use crate::core::objective::ObjectiveSpace;
 use crate::core::population::Population;
 use crate::core::problem::Problem;
 use crate::core::result::OptimizationResult;
-use crate::core::rng::{Rng, rng_from_seed};
+use crate::core::rng::rng_from_seed;
 use crate::metrics::hypervolume::hypervolume_nd_from_evaluations;
 use crate::pareto::front::{best_candidate, pareto_front};
 use crate::pareto::sort::non_dominated_sort;
@@ -264,7 +264,3 @@ mod tests {
     }
 }
 
-// Allow the unused-import warning from the `rng` import if certain feature
-// combinations don't use it.
-#[allow(dead_code)]
-fn _force_rng_use(_rng: &mut Rng) {}