feat(snake): modularize engine and add tournament tools

- Split active strategies, reusable engine code, core classes, and legacy snakes.
- Replace implicit snake imports with explicit module registrations.
- Extract Prism duel, spatial, and survival behavior into focused mixins.
- Improve duel scoring with food races, pressure, caches, and depth metrics.
- Add deterministic arena scenarios and paired seeded engine tournaments.
- Expand benchmark telemetry and bump Prism to version 1.3.0.
- Update documentation and tests for the new package layout and tooling.

snakes/engine/duel.py

@@ -0,0 +1,89 @@
+"""Reusable compact duel-search integration for Apex-style snakes."""
+
+from __future__ import annotations
+
+from snakes.engine.duel_search import BitboardDuelSearch
+
+class BitboardDuelMixin:
+  def _new_duel_search(
+      self, food_set: set, hazard_set: set, hazard_count: dict,
+      hazard_damage: int, width: int, height: int, deadline: float | None,
+    ) -> BitboardDuelSearch:
+      if self._duel_search_context is None:
+        self._duel_search_context = BitboardDuelSearch(
+          board=self._get_bb(width, height),
+          food=food_set,
+          hazards=hazard_set,
+          hazard_count=hazard_count,
+          hazard_damage=hazard_damage,
+          deadline=deadline,
+        )
+      return self._duel_search_context
+
+  def _minimax_candidate_id(
+      self, my_body: list, enemy_body: list, my_target: tuple[int, int],
+      food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, max_depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> tuple[float, int]:
+      """Resolve our selected move and every enemy reply simultaneously."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      adaptive_depth = max_depth
+      remaining = self._remaining_ms(deadline)
+      if remaining > 250:
+        adaptive_depth = min(7, max_depth + 1)
+      elif remaining < 120:
+        adaptive_depth = min(max_depth, 2)
+      return search.search_candidate(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_target=my_target,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        max_depth=adaptive_depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )
+
+  def _minimax_sim_id(
+      self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, max_depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> tuple[float, int]:
+      """Run iterative deepening with one reusable compact search context."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      return search.search(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        max_depth=max_depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )
+
+  def _minimax_sim(
+      self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> float:
+      """Compatibility entry point for tests and callers requesting one depth."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      return search.search_depth(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        depth=depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )