fix(core): use version agnostic get_fields (#33108)

Resolves a warning

Author: mdrxy

libs/core/langchain_core/tools/base.py

@@ -1324,8 +1324,7 @@ def get_all_basemodel_annotations(
     """
     # cls has no subscript: cls = FooBar
     if isinstance(cls, type):
-        # Gather pydantic field objects (v2: model_fields / v1: __fields__)
-        fields = getattr(cls, "model_fields", {}) or getattr(cls, "__fields__", {})
+        fields = get_fields(cls)
         alias_map = {field.alias: name for name, field in fields.items() if field.alias}
 
         annotations: dict[str, Union[type, TypeVar]] = {}
@@ -1402,7 +1401,7 @@ def _replace_type_vars(
         if type_ in generic_map:
             return generic_map[type_]
         if default_to_bound:
-            return type_.__bound__ or Any
+            return type_.__bound__ if type_.__bound__ is not None else Any
         return type_
     if (origin := get_origin(type_)) and (args := get_args(type_)):
         new_args = tuple(