community[patch]: Use get_fields adapter for pydantic (#25191)

Change all usages of __fields__ with get_fields adapter merged into
langchain_core.

Code mod generated using the following grit pattern:

```
engine marzano(0.1)
language python


`$X.__fields__` => `get_fields($X)` where {
    add_import(source="langchain_core.utils.pydantic", name="get_fields")
}
```

libs/community/langchain_community/chat_models/minimax.py

@@ -49,6 +49,7 @@ from langchain_core.runnables import Runnable, RunnableMap, RunnablePassthrough
 from langchain_core.tools import BaseTool
 from langchain_core.utils import convert_to_secret_str, get_from_dict_or_env
 from langchain_core.utils.function_calling import convert_to_openai_tool
+from langchain_core.utils.pydantic import get_fields
 
 logger = logging.getLogger(__name__)
 
@@ -399,7 +400,7 @@ class MiniMaxChat(BaseChatModel):
 
         default_values = {
             name: field.default
-            for name, field in cls.__fields__.items()
+            for name, field in get_fields(cls).items()
             if field.default is not None
         }
         default_values.update(values)