Optional arguments in `passive_transformation`

Before posting a feature request

[X] I have searched exisisting GitHub issues to make sure the feature request does not already exist.

Feature details

Both arguments mu and cov are required when calling thewalrus.symplectic.passive_transformation, even when only one of them is required. For example, to calculate the transformation for an covariance matrix only, a dummy-mu still needs to be created and passed.

dummy_mu = np.zeros([len(cov)])
_, cov = passive_transformation(dummy_mu, cov, T))

It would be good to be able to optionally pass the mu argument in the above case.

Implementation

No response

How important would you say this feature is?

1: Not important. Would be nice to have.

Additional information