void Start()
 {
     if (!uiManagerInstance)
     {
         uiManagerInstance = UIManager.GetInstance();
     }
     if (!pm)
     {
         pm = PoolManager.GetInstance();
     }
     if (!stateReference)
     {
         stateReference = State.GetInstance();
     }
     stateReference.WaveStateChanged += OnWaveStateChanged;
     stateReference.GameStateChanged += OnGameStateChanged;
     pm.CreateEnemyPool(enemyPrefab, 30);
     StartEnemies();
 }