Add explicit pooling classes for the Transformers backend (#25322)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
Co-authored-by: Isotr0py <mozf@mail2.sysu.edu.cn>

vllm/config/utils.py

@@ -4,6 +4,7 @@
 import ast
 import inspect
 import textwrap
+from collections.abc import Iterable
 from dataclasses import MISSING, Field, field, fields, is_dataclass, replace
 from typing import TYPE_CHECKING, Any, Protocol, TypeVar
 
@@ -52,6 +53,18 @@ def get_field(cls: ConfigType, name: str) -> Field:
         f"{cls.__name__}.{name} must have a default value or default factory.")
 
 
+def getattr_iter(object: object, names: Iterable[str], default: Any) -> Any:
+    """
+    A helper function that retrieves an attribute from an object which may
+    have multiple possible names. This is useful when fetching attributes from
+    arbitrary `transformers.PretrainedConfig` instances.
+    """
+    for name in names:
+        if hasattr(object, name):
+            return getattr(object, name)
+    return default
+
+
 def contains_object_print(text: str) -> bool:
     """
     Check if the text looks like a printed Python object, e.g.