improve efficiency of read.csv and write.csv

[hturner]

Discussed in #7

^{Originally posted by tdhock July 1, 2023}
Hi! I will not be attending the sprint, but I had a couple of ideas related to improving efficiency of read.csv and write.csv.

Probably the more important issue to address would be read.csv, which had time complexity quadratic in number of columns, see this issue for some empirical analysis:
tdhock/atime#8

Another issue was that write.csv uses linear memory, whereas other CSV writers use only constant memory (this is not that big of an issue though, because anyways you need linear memory to store the data in R before writing to CSV)
tdhock/atime#10

@gmbecker @bastistician may be able to help mentor? They worked on fixing a similar efficiency issue tdhock/atime#9