Replace PyTorch with Aesara

[aloctavodia]

I don't thing this is a priority at the moment. But at some point in the future, making this change will be beneficial. The two most obvious benefits will be removing one dependency, as aesara is already a Bambi dependency. And avoid duplicating code from bambi.

We could use this issue to track the functions that we actually need tom PyTorch that are currently absent from aesara. And then decided if those should be added upstream or we can add it as part of kulprit. I think we just require a couple of functions or so.