Support for instrument error whitening

[rlaugier]

Hi all, currently we are working on offering a nice clean interface to work with whitened observables, such as proposed in Ceau et al. 2019 and Laugier et al. 2023.

As of commit fbd3e0a, this is now offered through the extra module and the extra.Post class. This class helps you build w_ prefixed methods for the forward model that give whitened outputs.

This interface is still unstable, but we encourage everyone to try it out. Make sure you are following this thread to get news on this topic.