Update N3LO ad with 2512.10783

[felixhekhorn]

https://arxiv.org/pdf/2512.10783 provides

• a small update for $P_{gq}$
• splitting functions at $n_f=6$, i.e. this will remove

  eko/src/ekore/anomalous_dimensions/unpolarized/space_like/as4/fhmruvv/ggg.py

  Line 192 in 2e3a834

  raise NotImplementedError("nf=6 is not available at N3LO")

  and similar