Fixed Fisher Information Large N

- Fix: the FI estimation for Large N was not correct when using sigma_x directly. We needed to take the cov(mu) into account. Changed it so that sigma in the FI large N now corresponds to the mean of the diagonal elements of the KL covariance matrix (or the true measured one).
- Add: new function in sampler to compute the Large N Fisher Information nicely.
Generator/Reloader for fisher info single item

- Fix: Use the correct Large N Fisher information now.
- Add: Reloader for the Fisher information comparison for a single item. Does the same bar plot as in plots_paper_theo.fisher_information_1obj_2d()