Analytic covariance implementation

[adrien-laposta]

This PR includes a script to compute analytic covariance matrices using Namaster gaussian covariance tools.

It estimates the signal and noise contributions to the covariance on the data, following the combinatorics of the cross-bundle estimator.

This is a first working example of such a code, which needs to be further improved, particularly to account for the effect of filtering

[adrien-laposta]

Latest changes are

• Sim-based correction for the covariance estimated on TF simulations
• Generalized TF and pseudo CL to save unbinned estimates (used for the above correction)
• Generalization of covariance to account for inhomogeneous noise
• Pre-computing of covariance couplings (MPI parallelization)