Remove Python 3.9 support ahead of PyTorch 2.9 in v0.11.1 (#26416)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/config/utils.py

@@ -7,6 +7,7 @@ import inspect
 import textwrap
 from collections.abc import Iterable
 from dataclasses import MISSING, Field, field, fields, is_dataclass, replace
+from itertools import pairwise
 from typing import TYPE_CHECKING, Any, Protocol, TypeVar
 
 import regex as re
@@ -102,19 +103,6 @@ def get_attr_docs(cls: type[Any]) -> dict[str, str]:
     https://davidism.com/mit-license/
     """
 
-    def pairwise(iterable):
-        """
-        Manually implement https://docs.python.org/3/library/itertools.html#itertools.pairwise
-
-        Can be removed when Python 3.9 support is dropped.
-        """
-        iterator = iter(iterable)
-        a = next(iterator, None)
-
-        for b in iterator:
-            yield a, b
-            a = b
-
     try:
         cls_node = ast.parse(textwrap.dedent(inspect.getsource(cls))).body[0]
     except (OSError, KeyError, TypeError):