release method
Implementation
Future<bool> release(String appId, String playerId) async {
final key = _key(appId, playerId);
_generations[key] = (_generations[key] ?? 0) + 1;
final hadPending = _pending.containsKey(key);
final session = _sessions.remove(key);
if (session == null) return hadPending;
await session.dispose();
return true;
}