[3.13] gh-146333: Fix quadratic regex backtracking in configparser option parsing (GH-146399) (GH-148559)

Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly).
(cherry picked from commit 7e0a0be4097f9d29d66fe23f5af86f18a34ed7dd)

Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>