chore(internal): properly set __pydantic_private__ (#603)

Author: stainless-app[bot]

src/finch/_base_client.py

@@ -63,7 +63,7 @@
     ModelBuilderProtocol,
 )
 from ._utils import is_dict, is_list, asyncify, is_given, lru_cache, is_mapping
-from ._compat import model_copy, model_dump
+from ._compat import PYDANTIC_V2, model_copy, model_dump
 from ._models import GenericModel, FinalRequestOptions, validate_type, construct_type
 from ._response import (
     APIResponse,
@@ -208,6 +208,9 @@ def _set_private_attributes(
         model: Type[_T],
         options: FinalRequestOptions,
     ) -> None:
+        if PYDANTIC_V2 and getattr(self, "__pydantic_private__", None) is None:
+            self.__pydantic_private__ = {}
+
         self._model = model
         self._client = client
         self._options = options
@@ -293,6 +296,9 @@ def _set_private_attributes(
         client: AsyncAPIClient,
         options: FinalRequestOptions,
     ) -> None:
+        if PYDANTIC_V2 and getattr(self, "__pydantic_private__", None) is None:
+            self.__pydantic_private__ = {}
+
         self._model = model
         self._client = client
         self._options = options