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.

tests/snakes/test_PrismBattleSnake_GPT_5_6_Sol.py

@@ -2,11 +2,11 @@ import unittest
 from time import perf_counter
 
 from snakes import SnakeBuilder, get_snake_version
-from snakes.ApexBattleSnake import ApexBattleSnake
-from snakes.bitboard import BitBoard
-from snakes.bitboard_duel_search import BitboardDuelSearch
-from snakes.compact_survival_search import CompactSurvivalSearch
-from snakes.PrismBattleSnake_GPT_5_6_Sol import PrismBattleSnake_GPT_5_6_Sol
+from snakes.engine.bitboard import BitBoard
+from snakes.engine.duel_search import BitboardDuelSearch
+from snakes.engine.survival_search import CompactSurvivalSearch
+from snakes.strategies.apex import ApexBattleSnake
+from snakes.strategies.prism import PrismBattleSnake_GPT_5_6_Sol
 
 class TestBitBoard(unittest.TestCase):
 
@@ -52,8 +52,9 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     snake = PrismBattleSnake_GPT_5_6_Sol()
 
     self.assertEqual(snake.name, "PrismBattleSnake")
-    self.assertEqual(snake.version, "1.2.0")
-    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.2.0")
+    self.assertEqual(snake.version, "1.3.0")
+    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.3.0")
+    self.assertGreaterEqual(snake._planning_depth, 4)
     self.assertIsInstance(SnakeBuilder.build("PrismBattleSnake_GPT_5_6_Sol"), PrismBattleSnake_GPT_5_6_Sol)
 
   def test_bitboard_primitives_match_apex(self):
@@ -175,6 +176,21 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
 
     self.assertIs(snake._duel_search_context, first_context)
     self.assertGreater(first_context.nodes, 0)
+    self.assertGreater(first_context.completed_depth, 0)
+
+  def test_duel_evaluation_prioritizes_reachable_food_when_starving(self):
+    board = BitBoard(5, 3)
+    search = BitboardDuelSearch(
+      board=board, food={(2, 1)}, hazards=set(), hazard_count={},
+      hazard_damage=15, deadline=None,
+    )
+    my_body = [{"x": 0, "y": 1}, {"x": 0, "y": 0}]
+    enemy_body = [{"x": 4, "y": 1}, {"x": 4, "y": 0}]
+
+    hungry = search.search_depth(my_body, enemy_body, 15, 100, 0, set())
+    healthy = search.search_depth(my_body, enemy_body, 100, 100, 0, set())
+
+    self.assertLess(hungry, healthy)
 
   def test_compact_rollout_models_lethal_enemy_head_response(self):
     board = BitBoard(3, 3)
@@ -205,6 +221,7 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     search.search_selected(mine, enemies, (2, 1), depth=3)
 
     self.assertGreater(search.cache_hits, hits_before)
+    self.assertGreaterEqual(search.completed_depth, 3)
 
   def test_bitboard_duel_search_reuses_transpositions(self):
     board = BitBoard(5, 5)