Consider vendoring RTFDE #470
Description
When using extract_msg, I see warnings caused by RTFDE as described below
The issue has been open for a long time, marked as wontfix, with a PR to fix it open with no response
I have pinged it again but if there's no response, it may be good to vendor in the needed code from it to this repository. The warning was upgraded to SyntaxWarning in Python 3.14, soon it will fail entirely. The warnings themselves aren't ideal either so if RTFDE seems to not be getting maintained to fix it, it's probably a good idea to replace the dependency on it. And while I mention warning, it seems the behavior itself seems to be buggy, it should be using the utf-8 bytes, not the ascii string corresponding to the escape sequence as it currently does.