Generalize evolve to accommodate two EKOs

[Radonirinaunimi]

Beyond the standard unpolarized proton-proton case, it may occur that two initial states need to be evolved differently using un-/polarized time-/space-like evolutions. This therefore requires some changes in how the EKOs are applied to the grids.

[giacomomagni]

#181 has addressed the poalrized/ unpolarized convolutions.

@t7phy do you want me to take care also of UnpolFF cases or better wait for the new metadata format and close this issue?

[t7phy]

@giacomomagni indeed we need to add the possibility for UnpolFF too, and it would be nice if you added it. I think (not fully sure) that the only difference when going to new file format will be that this info will be carried by the file intrinsically as opposed to the metadata, but when that happens we will anyway have to change how pineko determines the convolution type.
So in short, yes please add the UnpolFF for the time being and then once the v1 format is finalized, we can modify it for thhe the types as needed.

[giacomomagni]

All the timelike grids follows the current convention (ie they have convolution_type_1 ecc ),
we don't need to support older versions right?

[t7phy]

yes, only the current convention is needed