Fix SyntaxWarnings due to invalid escape sequences (Python 3.12 compatibility)

Hi, I'm the Debian maintainer for python-jieba. While testing with recent Python versions, we noticed several SyntaxWarning: invalid escape sequence warnings.

I've attached a patch that fixes these by using raw strings for regex. We are already using this fix in Debian.

0002-fix-syntax-warnings.patch

Best regards, Arian Ott