add_case/add_row silently converts factors to strings

[vorpalvorpal]

If you provide a character vector to a column that is currently a factor add_case changes the column class to character.

tibble(col = fct(NA_character_, levels = c("A", "B"))) |>
    add_case(col = "A")

I feel like this should, at the very least, produce a warning rather than just silently changing the class of the column. Possibly it should even change "A" to to fct("A") with a warning.