Match the body of a quoted field without possessive quantifiers

They were added in 3.11.  An unrolled loop is unambiguous at every
position, so it does not backtrack either.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/csv.py

@@ -269,12 +269,14 @@ def _guess_quote_and_delimiter(self, data, delimiters):
         doublequote = False
         if delim:
             dq_regexp = re.compile(
-                    r"(?:(?<=%(delim)s)|^)%(space)s%(quote)s"     # ,"
-                    r"((?:%(quote)s%(quote)s|[^%(quote)s]++)*+)"  # the body
-                    r"%(quote)s(?:%(delim)s|$)"                   # ",
+                    r"(?:(?<=%(delim)s)|^)%(space)s%(quote)s"       # ,"
+                    # The body, as an unrolled loop: it is unambiguous,
+                    # so it does not backtrack.
+                    r"([^%(quote)s]*(?:%(quote)s%(quote)s[^%(quote)s]*)*)"
+                    r"%(quote)s(?:%(delim)s|$)"                     # ",
                     % {'delim': re.escape(delim), 'quote': quotechar,
                        # Skipping spaces after a space rescans them.
-                       'space': ' *+' if delim != ' ' else ''},
+                       'space': ' *' if delim != ' ' else ''},
                     re.MULTILINE)
             dquotechar = quotechar * 2
             doublequote = any(dquotechar in m[1]