Preprint updated version

This release incorporates many new functionalities, and it allows to run all analyses in the preprint, unlike previous releases.

• The model using both means and covariances was implemented. The SQFA class now refers to this model
• The old SQFA class is now called SecondMomentsSQFA
• The Fisher-Rao lower bounds were implemented
• A method to initialize the filters using pca was included
• The documentation tutorials were tidied and updated to include these functionalities
• There are new options to the inputs of the fitting functions