Hi, thank you for this great library.

I have a question about the vector Env. The shape of my customized Env's state depends on its size. For example, Env(size=n) will return nx.Graph() with n nodes as its state. However, when I create vector Env with different nodes num, it will raise an error since states with different sizes cannot be stacked (at https://github.com/thu-ml/tianshou/blob/master/tianshou/env/venvs.py#L166). And it seems that the Batch class does not support states with different sizes either.

So, is there an easy way to make the vector Env collect states with different sizes?

Thank you very much!