langchain-community[major]: Upgrade community to pydantic 2 (#26011)

This PR upgrades langchain-community to pydantic 2.


* Most of this PR was auto-generated using code mods with gritql
(https://github.com/eyurtsev/migrate-pydantic/tree/main)
* Subsequently, some code was fixed manually due to accommodate
differences between pydantic 1 and 2

Breaking Changes:

- Use TEXTEMBED_API_KEY and TEXTEMBEB_API_URL for env variables for text
embed integrations:
cbea780492

Other changes:

- Added pydantic_settings as a required dependency for community. This
may be removed if we have enough time to convert the dependency into an
optional one.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/community/langchain_community/retrievers/milvus.py

@@ -6,8 +6,8 @@ from typing import Any, Dict, List, Optional
 from langchain_core.callbacks import CallbackManagerForRetrieverRun
 from langchain_core.documents import Document
 from langchain_core.embeddings import Embeddings
-from langchain_core.pydantic_v1 import root_validator
 from langchain_core.retrievers import BaseRetriever
+from pydantic import model_validator
 
 from langchain_community.vectorstores.milvus import Milvus
 
@@ -93,8 +93,9 @@ class MilvusRetriever(BaseRetriever):
     store: Milvus
     retriever: BaseRetriever
 
-    @root_validator(pre=True)
-    def create_retriever(cls, values: Dict) -> Dict:
+    @model_validator(mode="before")
+    @classmethod
+    def create_retriever(cls, values: Dict) -> Any:
         """Create the Milvus store and retriever."""
         values["store"] = Milvus(
             values["embedding_function"],