refactor(langchain): refactor unit test stub classes (#32209)

See
https://github.com/langchain-ai/langchain/pull/32098#discussion_r2225961563

libs/langchain/tests/unit_tests/stubs.py

@@ -1,48 +1,23 @@
-from typing import Any
-
-from langchain_core.documents import Document
-from langchain_core.messages import AIMessage, AIMessageChunk, HumanMessage
+from langchain_core.messages import AIMessage, AIMessageChunk
+from pydantic import BaseModel
 
 
-class AnyStr(str):
-    __slots__ = ()
-
+class _AnyIDMixin(BaseModel):
     def __eq__(self, other: object) -> bool:
-        return isinstance(other, str)
+        if isinstance(other, BaseModel):
+            dump = self.model_dump()
+            dump.pop("id")
+            other_dump = other.model_dump()
+            other_dump.pop("id")
+            return dump == other_dump
+        return False
 
-    __hash__ = str.__hash__
+    __hash__ = None  # type: ignore[assignment]
 
 
-# The code below creates version of pydantic models
-# that will work in unit tests with AnyStr as id field
-# Please note that the `id` field is assigned AFTER the model is created
-# to workaround an issue with pydantic ignoring the __eq__ method on
-# subclassed strings.
+class _AnyIdAIMessage(AIMessage, _AnyIDMixin):
+    """AIMessage with any ID."""
 
 
-def _AnyIdDocument(**kwargs: Any) -> Document:
-    """Create a document with an id field."""
-    message = Document(**kwargs)
-    message.id = AnyStr()
-    return message
-
-
-def _AnyIdAIMessage(**kwargs: Any) -> AIMessage:
-    """Create ai message with an any id field."""
-    message = AIMessage(**kwargs)
-    message.id = AnyStr()
-    return message
-
-
-def _AnyIdAIMessageChunk(**kwargs: Any) -> AIMessageChunk:
-    """Create ai message with an any id field."""
-    message = AIMessageChunk(**kwargs)
-    message.id = AnyStr()
-    return message
-
-
-def _AnyIdHumanMessage(**kwargs: Any) -> HumanMessage:
-    """Create a human with an any id field."""
-    message = HumanMessage(**kwargs)
-    message.id = AnyStr()
-    return message
+class _AnyIdAIMessageChunk(AIMessageChunk, _AnyIDMixin):
+    """AIMessageChunk with any ID."""