Remove sympy dependency

[vprusso]

As sympy is a required install but only used for one function, it might be ideal to use another non-sympy approach to reduce the need to require sympy as a dependency. https://github.com/vprusso/toqito/blob/39bad5dd0181758ba8696742bae4c7349eb25861/toqito/states/mutually_unbiased_basis.py#L4

We could then remove the dependency from the toml file: https://github.com/vprusso/toqito/blob/39bad5dd0181758ba8696742bae4c7349eb25861/pyproject.toml#L48

and from the requirements: https://github.com/vprusso/toqito/blob/39bad5dd0181758ba8696742bae4c7349eb25861/docs/requirements.txt#L3