Fix "SyntaxWarning: invalid escape sequence" warnings

[jiripospisil]

Hello, fixed a few warnings emitted when using Python 3.12.

From: https://docs.python.org/3.14/whatsnew/3.12.html#other-language-changes

A backslash-character pair that is not a valid escape sequence now generates a SyntaxWarning, instead of DeprecationWarning. For example, re.compile("\d+.\d+") now emits a SyntaxWarning ("\d" is an invalid escape sequence, use raw strings for regular expression: re.compile(r"\d+.\d+")). In a future Python version, SyntaxError will eventually be raised, instead of SyntaxWarning. (Contributed by Victor Stinner in gh-98401.)

$ python --version
Python 3.12.3

$ python -m compileall -f -q .
./marcel/doc/help_color.py:16: SyntaxWarning: invalid escape sequence '\{'
  HELP = '''
./marcel/doc/help_operator.py:16: SyntaxWarning: invalid escape sequence '\{'
  HELP = '''
./test/test_ops.py:271: SyntaxWarning: invalid escape sequence '\|'
  TEST.run('gen 75 | select (x: x in (18, 36, 73)) | red \|',

[geophile]

Looks good, thank you.

[geophile]

Could you please bump the minor version to go along with this change? It's in marcel/marcel/version.py.

[jiripospisil]

Could you please bump the minor version to go along with this change? It's in marcel/marcel/version.py.

Done.