Fix escape sequences treated as unicode laterals

Fix escape sequences treated as unicode laterals

Since Python 3.6, unrecognized escape sequences produce a DeprecationWarning.
Since Python 3.12, unrecognized escape sequences produce a SyntaxWarning.
In a future Python version they will be eventually a SyntaxError.

https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals

Fix these by using raw string literals.