Standardize CKM matrix about pinefarm

[felixhekhorn]

it was just historically a string since we were bound to sqlite ...

in yadism we wrote a conversion to support that https://github.com/NNPDF/yadism/blob/9db321d2f3496d8ba85ee9b7587b1b7231d8ecc3/src/yadism/coefficient_functions/coupling_constants.py#L460

[felixhekhorn]

do you want to do a list + .reshape(3,3) or directly a matrix?

[scarlehoff]

I see, if we have the conversion in separate programs we might as well convert it to a list everywhere.
Maybe directly a 3x3 matrix makes more sense? but that part I don't really mind