Sympy version not compatible with Torch

[peterbjohnson]

We require Sympy 1.12:

toolkit-python/pyproject.toml

Line 16 in f613e97

sympy = "1.12"

But there are more recent versions. Specifically, the Torch library is only compatible with SymPy >=1.13.3, which makes them incompatible. I doubt there are breaking changes between 1.12 and 1.13 that will affect us. We need to check though, and if it's OK, we should update pyporject.toml in the toolkit repo, and update the package (I guess it goes straight into Shimmy? I'm not sure how).