[Bug]: Error when using a Chat with gemini model: ModuleNotFoundError: No module named 'transformers'

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### RAGFlow workspace code commit ID

v0.20.1 slim

### RAGFlow image version

v0.20.1 slim

### Other environment information

```Markdown

```

### Actual behavior

When creating a chat and setting any chat model from gemini, i get this error:

When using the deepseek model this does not happen:

### Expected behavior

_No response_

### Steps to reproduce

```Markdown
Create a chat and set the model to any gemini chat model
Try to have a conversation
```

### Additional information

````
Traceback (most recent call last):
File "/ragflow/api/apps/conversation_app.py", line 203, in stream
for ans in chat(dia, msg, True, **req):
File "/ragflow/api/db/services/dialog_service.py", line 256, in chat
for ans in chat_solo(dialog, messages, stream):
File "/ragflow/api/db/services/dialog_service.py", line 174, in chat_solo
for ans in chat_mdl.chat_streamly(prompt_config.get("system", ""), msg, dialog.llm_setting):
File "/ragflow/api/db/services/llm_service.py", line 413, in chat_streamly
for txt in chat_partial(**kwargs):
File "/ragflow/rag/llm/cv_model.py", line 523, in chat_streamly
from transformers import GenerationConfig
ModuleNotFoundError: No module named 'transformers'
````

Start with rag/llm/cv_model.py at the chat_streamly path shown in the traceback, then follow the calls through api/apps/conversation_app.py, api/db/services/dialog_service.py, and api/db/services/llm_service.py. Reproduce the issue by creating a chat with a Gemini model and verify that conversation streaming completes without the transformers import error.

Written by the indexing model from the issue text.