core: fix CommaSeparatedListOutputParser to handle columns that may contain commas in it (#26365)

- **Description:**
Currently CommaSeparatedListOutputParser can't handle strings that may
contain commas within a column. It would parse any commas as the
delimiter.
Ex. 
"foo, foo2", "bar", "baz"

It will create 4 columns: "foo", "foo2", "bar", "baz"

This should be 3 columns:

"foo, foo2", "bar", "baz"

- **Dependencies:**
Added 2 additional imports, but they are built in python packages.

import csv
from io import StringIO

- **Twitter handle:** @jkyamog

- [ ] **Add tests and docs**: 
1. added simple unit test test_multiple_items_with_comma

---------

Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/core/langchain_core/output_parsers/list.py

@@ -1,9 +1,11 @@
 from __future__ import annotations
 
+import csv
 import re
 from abc import abstractmethod
 from collections import deque
 from collections.abc import AsyncIterator, Iterator
+from io import StringIO
 from typing import Optional as Optional
 from typing import TypeVar, Union
 
@@ -162,7 +164,14 @@ class CommaSeparatedListOutputParser(ListOutputParser):
         Returns:
             A list of strings.
         """
-        return [part.strip() for part in text.split(",")]
+        try:
+            reader = csv.reader(
+                StringIO(text), quotechar='"', delimiter=",", skipinitialspace=True
+            )
+            return [item for sublist in reader for item in sublist]
+        except csv.Error:
+            # keep old logic for backup
+            return [part.strip() for part in text.split(",")]
 
     @property
     def _type(self) -> str: