Python 3.15 Support

Python 3.15 officially releases in less than a month, and I'm hoping for us to get Python 3.15 out with Gymnasium a lot sooner in the cycle compared to how long Python 3.14 took, so that other Farama projects can update to 3.15 sooner. Without checking every single dependency, at least Numpy and pygame-ce already support Python 3.15 with current versions, and the ALE we control ourselves.