move `separate_multiplicative` key outside `sampling` key in runcard

this fixes vp-setupfit since there separate_multiplicative was not parsed from the sampling key and thus it was not found

Avoid idle gpu

epoch.

Avoids memory overhead by only combining up to 100 steps into one epoch,
and not changing anything when using only 1 replica (i.e. on CPU).

Polarised Jet commondata implementation

Adds integrability datasets for DV and DV3

Allow for F1 FKtables in G1F1 ratio

Polarised scale variation theories

Merge branch 'polarised-scale-variation' of https://github.com/NNPDF/nnpdf into polarised-scale-variation