Skip requiring `subgroup_traces` be a `Group`
Skip requiring `subgroup_traces` be a `Group`

As we are only storing one value as an `Array` in `subgroup_traces`,
there is no need to create a `Group` beforehand. In fact, the `Group`
merely is removed during storage of the traces anyways. So skip making
`subgroup_traces` a `Group` altogether.

DudLab/nanshe_workflow,nanshe-org/nanshe_workflow