Freeze dependencies to avoid backward compatibility issues

When launching the space, I ran into the following `Runtime error`:
```
Exit code: 1. Reason: Traceback (most recent call last):
File "/home/user/app/app.py", line 3, in <module>
from smolagents import GradioUI, CodeAgent, HfApiModel
ImportError: cannot import name 'HfApiModel' from 'smolagents' (/usr/local/lib/python3.10/site-packages/smolagents/__init__.py)
```

Freezing all libraries' versions works for me. Please see my space [here](https://huggingface.co/spaces/gabzer/Unit_3_Agentic_RAG).

requirements.txt

@@ -1,5 +1,5 @@
-datasets 
-smolagents 
-langchain-community 
-rank_bm25
-duckduckgo-search
+datasets==3.1.0
+smolagents==1.18
+langchain-community==0.3.29
+rank-bm25==0.2.2
+duckduckgo-search==8.1.1