[R] Fix performance regression from cpp11::r_string #26382
Description
On a taxi CSV read demo, reading a data.frame went from ~7 seconds to ~30 seconds. One of the cpp11 changes was identified to be a cause, and reverting it recovered the lost performance.
Reporter: Neal Richardson / @nealrichardson
Assignee: Neal Richardson / @nealrichardson
PRs and other links:
Note: This issue was originally created as ARROW-10399. Please see the migration documentation for further details.