The virtual base of
FineMappingMethodsParam and
TwasWeightsMethodsParam: which methods a pipeline runs,
and each one's engine arguments.
Three slots rather than one because a method running on both data paths
reaches a different engine on each — lasso is glmnet on
individual-level data and lassosum on summary statistics — so one bag
of arguments per method cannot serve a MultiStudyQtlDataset
carrying both. methods holds entries whose input path need not
be stated; qtlDatasetMethods and qtlSumStatsMethods hold
the ones that must state it. Naming a method selects it.