[writing] provide openxlsx2.export_with_pugi = FALSE option

[JanMarvin]

This works on my linux machine with 32gb of memory, whereas it ~~fails to export with pugixml due to the dom blowing up~~ needs approximately 6gb more with pugixml.

library(openxlsx2)

n <- 10000
k <- 1000
mm <- matrix(rnorm(n * k), ncol = n, nrow = k)

temp <- temp_xlsx()

options("openxlsx2.export_with_pugi" = FALSE)
write_xlsx(x = mm, temp)

Interestingly reading does not requires that much memory.

wb <- openxlsx2::wb_load(temp)