fix: preserve gameplay data and correct duel evaluation

- Preserve snake customizations across database migrations and merges.
- Lazily load optional storage backends for SQLite maintenance scripts.
- Match Apex territory and nearest-food tie-breaking semantics.
- Resolve duel occupancy after simultaneous movement and food growth.
- Recompute simulated head-to-head danger after body growth.
- Add regression coverage and declare the aiofiles dependency.

scripts/migrate_gameplay_database.py

@@ -144,20 +144,27 @@ def copy_game_snakes(source:sqlite3.Connection, destination:sqlite3.Connection,
     SELECT 1 FROM sqlite_master WHERE type = 'table' AND name = 'game_snakes'
   """).fetchone() is not None
   if has_game_snakes:
-    cursor = source.execute("""
-      SELECT game_id, snake_id, snake_name, is_you
+    columns = object_columns(source, "game_snakes")
+    customizations = (
+      "COALESCE(customizations_json, '{}') AS customizations_json"
+      if "customizations_json" in columns else "'{}' AS customizations_json"
+    )
+    cursor = source.execute(f"""
+      SELECT game_id, snake_id, snake_name, is_you, {customizations}
       FROM game_snakes ORDER BY game_id, snake_id
     """)
   else:
     cursor = source.execute("""
-      SELECT game_id, snake_id, MAX(snake_name), MAX(is_you)
+      SELECT game_id, snake_id, MAX(snake_name), MAX(is_you),
+        '{}' AS customizations_json
       FROM snake_turns
       GROUP BY game_id, snake_id
       ORDER BY game_id, snake_id
     """)
   sql = """
-    INSERT INTO game_snakes (game_id, snake_id, snake_name, is_you)
-    VALUES (?, ?, ?, ?)
+    INSERT INTO game_snakes (
+      game_id, snake_id, snake_name, is_you, customizations_json
+    ) VALUES (?, ?, ?, ?, ?)
   """
   count = 0
   while rows := cursor.fetchmany(batch_size):