cqltypes: fix SyntaxWarning for invalid escape sequence in UDT names

In cqltype_to_python(), double-quoted UDT names containing backslashes
(e.g. '"!@#$%^&*()[]\ frozen >>>") were passed to ast.literal_eval
without escaping, producing SyntaxWarning on Python 3.12+:

  SyntaxWarning: "\ " is an invalid escape sequence

Escape backslashes before wrapping the token for ast.literal_eval.
The reverse operation already exists in python_to_cqltype() at line 159.

Author: mykaul

cassandra/cqltypes.py

@@ -130,7 +130,7 @@ def cqltype_to_python(cql_string):
         (r'<', lambda s, t: ', ['),
         (r'>', lambda s, t: ']'),
         (r'[, ]', lambda s, t: t),
-        (r'".*?"', lambda s, t: "'{}'".format(t)),
+        (r'".*?"', lambda s, t: "'{}'".format(t.replace('\\', '\\\\'))),
     ))
 
     scanned_tokens = scanner.scan(cql_string)[0]