Consider using unprefixed names by default when returning a df from `epi[x]_slide`

[brookslogan]

[brookslogan]

This is already possible via names_sep=NULL. But I wonder if it will be more convenient to change to no-name-prefix by default and remove names_sep instead, matching more closely with dplyr's group_modify, reframe, summarize, etc., plus also having tidyeval expressions returning data frames be put into tibble-type columns (column bundles).