NS-Gym: A Comprehensive and Open-Source Simulation Framework for Non-Stationary Markov Decision Processes - Keplinger, Nathaniel S.; Luo, Baiting; Zhang, Yunuo; Wray, Kyle H; Laszka, Aron; Dubey, Abhishek; Mukhopadhyay, Ayan (Advances in Neural Information Processing Systems, 2025)