Extract attribute. Returns NA if none
Examples
attr(mtcars$mpg, "label") <- "testing"
do.call(c, sapply(mtcars, get_attr))
#> $mpg.label
#> [1] "testing"
#>
if (FALSE) { # \dontrun{
mtcars |>
numchar2fct(numeric.threshold = 6) |>
ds2dd_detailed()
} # }