perf(battlesnake): defer ordered lifecycle bookkeeping

- Acknowledge start and end without waiting for persistence or dashboards.
- Keep runtime creation and finished-game removal on the response path.
- Serialize start, turn, and end bookkeeping per game in Quart tasks.
- Capture turn thinking before scheduling deferred persistence.
- Defer start metrics, logging, and stale-game pruning.
- Run legacy history exports in a worker thread.
- Record results and end metrics even when history export fails.
- Drain pending bookkeeping before closing storage during shutdown.
- Test sub-500 ms responses with slow backends and real SQLite.
- Cover event ordering, export failures, and rejected user agents.

server/services/game_runtime.py

@@ -18,7 +18,7 @@ class GameRuntimeService:
   def attach_metrics_collector(self, metrics_collector:MetricsCollector) -> None:
     self.metrics_collector = metrics_collector
 
-  async def create_game_board(self, game_state:dict) -> GameBoard:
+  async def create_game_board(self, game_state:dict, publish_metrics:bool=True) -> GameBoard:
     game_id = game_state['game']['id']
     new_game_board = GameBoard(
       game_id=game_id,
@@ -34,7 +34,7 @@ class GameRuntimeService:
     self.running_games[game_id] = new_game_board
     self.game_move_counts[game_id] = 0
     self.game_last_seen_unix[game_id] = int(time.time())
-    if self.metrics_collector is not None:
+    if publish_metrics and self.metrics_collector is not None:
       await self.metrics_collector.record_game_started(len(self.game_last_seen_unix))
     return new_game_board