5994b4f76a
str.lstrip("r/") treats its argument as a character set, stripping
leading r and / repeatedly. Subreddits starting with 'r' (e.g. r/robotics,
r/ruby) were silently mangled to 'obotics' / 'uby'. Replace with
str.removeprefix("r/") at all four call sites. Python 3.9+ pattern is
safe here — project requires 3.12. Closes #288.
Co-authored-by: Alex Key <alexanderkey0508@gmail.com>