Don't remove units attribute of difftime when cleaning data on pre-process

[mstackhouse]

library(lubridate)

x <- ymd("2024-01-01") - ymd("2024-01-02")
attributes(x)

Tplyr/R/prebuild.R

Line 13 in 1fa6c4c

built_target <- clean_attr(target)

Tplyr/R/utils.R

Line 260 in 1fa6c4c

clean_attr <- function(dat) {