perf(snake): cache survival rollout state

- Cache occupancy bitboards for repeated multiplayer rollout positions.
- Memoize position evaluations to avoid duplicate flood-fill calculations.
- Reuse shared values while ranking simultaneous enemy responses.
- Include evaluation hits in Prism rollout telemetry.
- Document the optimization and bump Prism to version 1.4.0.

tests/snakes/test_PrismBattleSnake_GPT_5_6_Sol.py

@@ -52,8 +52,8 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     snake = PrismBattleSnake_GPT_5_6_Sol()
 
     self.assertEqual(snake.name, "PrismBattleSnake")
-    self.assertEqual(snake.version, "1.3.0")
-    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.3.0")
+    self.assertEqual(snake.version, "1.4.0")
+    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.4.0")
     self.assertGreaterEqual(snake._planning_depth, 4)
     self.assertIsInstance(SnakeBuilder.build("PrismBattleSnake_GPT_5_6_Sol"), PrismBattleSnake_GPT_5_6_Sol)
 
@@ -221,6 +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.assertGreater(search.evaluation_cache_hits, 0)
     self.assertGreaterEqual(search.completed_depth, 3)
 
   def test_bitboard_duel_search_reuses_transpositions(self):