fix: fill_flattened broadcasting of non user kwargs

[Jammf]

When usingfill_flattened with multiple args and either the weight or sample kwargs, it tries to broadcast the keys of non_user_kwargs instead of the values, leading to kwargs trying to fill the histogram with the stringified kwarg name instead of its value (such as the sample kwarg attempting to fill the array with ["sample", "sample", "sample", "sample"]). This PR changes that behavior to insert the values instead.