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/__init__.py

@@ -1,40 +1,61 @@
 import importlib
+from dataclasses import dataclass
 
+@dataclass(frozen=True, slots=True)
+class SnakeRegistration:
+  module: str
+  version: str
+
+SNAKE_REGISTRATIONS = {
+  "TemplateSnake": SnakeRegistration("snakes.core.template", "1.0.0"),
+  "ApexBattleSnake": SnakeRegistration("snakes.strategies.apex", "1.0.0"),
+  "PrismBattleSnake_GPT_5_6_Sol": SnakeRegistration(
+    "snakes.strategies.prism", "1.3.0"
+  ),
+  "DummSnake": SnakeRegistration("snakes.legacy.DummSnake", "1.0.0"),
+  "LogicSnake": SnakeRegistration("snakes.legacy.LogicSnake", "1.1.0"),
+  "MasterSnake": SnakeRegistration("snakes.legacy.MasterSnake", "1.2.0"),
+  "BetterMasterSnake": SnakeRegistration("snakes.legacy.BetterMasterSnake", "1.3.0"),
+  "BestBattleSnake": SnakeRegistration("snakes.legacy.BestBattleSnake", "2.6.0"),
+  "TrainedBattleSnake": SnakeRegistration(
+    "snakes.legacy.TrainedBattleSnake", "0.1.0"
+  ),
+  "UltimateBattleSnake": SnakeRegistration(
+    "snakes.legacy.UltimateBattleSnake", "4.5.0"
+  ),
+  "SupremeBattleSnake_ClaudeOpus4_6": SnakeRegistration(
+    "snakes.legacy.SupremeBattleSnake_ClaudeOpus4_6",
+    "1.0.0",
+  ),
+}
+
+# Backward-compatible public version map.
 SNAKE_REGISTRY = {
-  "TemplateSnake": "1.0.0",
-  "DummSnake": "1.0.0",
-  "LogicSnake": "1.1.0",
-  "MasterSnake": "1.2.0",
-  "BetterMasterSnake": "1.3.0",
-  "BestBattleSnake": "2.6.0",
-  "TrainedBattleSnake": "0.1.0",
-  "UltimateBattleSnake": "4.5.0",
-  "ApexBattleSnake": "1.0.0",
-  "SupremeBattleSnake_ClaudeOpus4_6": "1.0.0",
-  "PrismBattleSnake_GPT_5_6_Sol": "1.2.0",
+  name: registration.version for name, registration in SNAKE_REGISTRATIONS.items()
 }
 
 DEFAULT_SNAKE_CONFIG = {
-  'apiversion': '1',
-  'author': '',
-  'color': '#888888',
-  'head': 'default',
-  'tail': 'default',
+  "apiversion": "1",
+  "author": "",
+  "color": "#888888",
+  "head": "default",
+  "tail": "default",
 }
 
-def build_snake(selected_snake:str):
-  if selected_snake not in SNAKE_REGISTRY:
+
+def build_snake(selected_snake: str):
+  registration = SNAKE_REGISTRATIONS.get(selected_snake)
+  if registration is None:
     raise ValueError(f"Unknown snake: {selected_snake}")
 
-  snake_module = importlib.import_module(f"snakes.{selected_snake}")
+  snake_module = importlib.import_module(registration.module)
   snake_class = getattr(snake_module, selected_snake)
   return snake_class()
 
-def get_snake_version(selected_snake:str) -> str|None:
-  version = SNAKE_REGISTRY.get(selected_snake)
-  if version is None:
-    return None
-  return str(version)
+def get_snake_version(selected_snake: str) -> str | None:
+  registration = SNAKE_REGISTRATIONS.get(selected_snake)
+  return registration.version if registration is not None else None
+
 
 class SnakeBuilder:
   @classmethod
@@ -42,5 +63,5 @@ class SnakeBuilder:
     return build_snake(selected_snake)
 
   @classmethod
-  def get_version(self, selected_snake:str) -> str|None:
+  def get_version(self, selected_snake: str) -> str | None:
     return get_snake_version(selected_snake)