unity detect mouse double click with input
private float lastClickTime;
public float catchTime = 0.25f;
void Update ()
{
    if(Input.GetButtonDown("Fire1"))
    {
        if(Time.time - lastClickTime < catchTime)
        {
            //double click
            print("Double click");
        }
        else
        {
            //normal click
        }
        lastClickTime = Time.time;
    }
}