feat(ga): tournament selection + elitism

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/ga/selection.py

@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+import random
+
+from ..genome.hypothesis import HypothesisAgentGenome
+
+
+def tournament_select(
+    population: list[HypothesisAgentGenome],
+    fitnesses: dict[str, float],
+    k: int,
+    rng: random.Random,
+) -> HypothesisAgentGenome:
+    """Estrae k individui random e restituisce il migliore."""
+    if k < 1:
+        raise ValueError("k must be >= 1")
+    if not population:
+        raise ValueError("empty population")
+    candidates = rng.sample(population, k=min(k, len(population)))
+    return max(candidates, key=lambda g: fitnesses.get(g.id, 0.0))
+
+
+def elite_select(
+    population: list[HypothesisAgentGenome],
+    fitnesses: dict[str, float],
+    k: int,
+) -> list[HypothesisAgentGenome]:
+    """Restituisce i k genomi con fitness più alta."""
+    sorted_pop = sorted(population, key=lambda g: fitnesses.get(g.id, 0.0), reverse=True)
+    return sorted_pop[:k]