Polarized matching

[giacomomagni]

Here we provide the polarised matching conditions for g1 .

@t7phy you can find some TODO where you should add the x-space expression obtained with Mathematica.
If you can avoid repeating (as I mentioned I think the LL part will be same as the unpolarised one, but plese double check!! )

[giacomomagni]

Hi @adrianneschauss, @Radonirinaunimi, @t7phy, @felixhekhorn I've added the x-space matching conditions.

@t7phy To perform any meaningful test we need to update the eko dependency since the polarised matching is included only in eko^=0.13.0. We will do it soon, but in another PR

As usual I found out the weird factor of 2 in splitting functions definition comparing https://arxiv.org/pdf/2211.15337.pdf to the rest of our references, maybe with this PR we will sort this out and be able to provide a cross check also on eko implementation. In any case also here the possibility to benchmark FONLL are quite limited.

@adrianneschauss with this PR we should be able to compute g1 FONLL, now we need to check if it make sense!

[giacomomagni]

@adrianneschauss I believe this PR should be ready to go and you should be able to produce the plot Juan asked for
(note you need to use the latest version of eko).

Generally @felixhekhorn, @Radonirinaunimi and @alecandido I think it's quite minimal that we can consider to merge it as well in the main Yadism, even if we are aware other PR are going in different directions. What do you think?