Upgrade plans to later Python & Gymnasium

Hi there

I came across this fork https://github.com/andrewsiah/spinningup_pytorch and then created a new fork to run things on a slightly newer python 3.13 and Gymnasium. I pushed the changes to a new repo https://github.com/keivanzavari/spinningup.

I am not sure if this repo is maintained or not. In case it is, maybe I can make a proper PR to merge things upstream. Otherwise I thought for some future readers, this message may help.