Support hms writing

[JanMarvin]

Currently this

library(openxlsx2)
hms_time <- hms::as_hms("12:13:14")
wb <- wb_workbook()$add_worksheet()$add_data(x = hms_time, colNames = FALSE)

leads to a corrupt xlsx file. This is because we treat hms_time as a simple numeric. Unfortunately there appears to be some under the hood conversion that results in us writing 12:13:14 into a field where the open xml standard allows only numerical values.

To avoid a dependency on hms (unfortunately there is no such function in R base), we return hms columns if hms is loaded and strings otherwise.

library(openxlsx2)

## with hms
library(hms)

x <- hms::as_hms("12:13:14")

wb <- wb_workbook()$add_worksheet()$add_data(x = x, colNames = FALSE)

z <- wb_to_df(wb, colNames = FALSE, convert = TRUE)
z
#>          A
#> 1 12:13:14
class(z$A)
#> [1] "hms"      "difftime"
attr(z, "tt")
#>   A
#> 1 h

## without hms
detach("package:hms", unload = TRUE)

x <- hms::as_hms("12:13:14")

wb <- wb_workbook()$add_worksheet()$add_data(x = x, colNames = FALSE)

z <- wb_to_df(wb, colNames = FALSE, convert = FALSE)
z
#>          A
#> 1 12:13:14
class(z$A)
#> [1] "character"
attr(z, "tt")
#>   A
#> 1 h