How did people cut their toe and fingernails before we got nail clippers after the industrial revolution?
Would they have had a fair amount of ingrown toenails, especially in the colder regions where feet had to be kept wrapped up?
With a paring knife. That's why nail parings are called, well, nail parings.
Also, there were nippers similar to modern yarn cutters which were in common use since Roman times. Yarn cutters look like this:
Scraping the tip of your nails across a pocket knife blade. My grandfather does it all the time. It's similar to how some nail files work.