A classic case of the win described by
https://build123d.readthedocs.io/en/latest/algebra_performance.html
Before, these test cases took 1.26s and 0.28s, making them the slowest
and 8th-slowest test cases in the entire repo according to `py.test
--durations=10`, and a full pytest run takes 12.31s.
After, these test cases both take 0.09s, and a full run takes 10.90s.
Also added `prof/` to `.gitignore` because using pytest's
`--profile{-svg}` options creates this directory but it is unlikely to
be usefully tracked by git.
