[misc] Compatibility Issue with Python 3.9 in FSDP Worker for LLaMA Model

[uygnef]

Fix: Compatibility Issue with Python 3.9 in FSDP Worker for LLaMA Model

When running the LLaMA model in the FSDP worker, an ImportError occurs due to the use of the Unpack type from the typing module. This type is only available in Python 3.11 and later, but the current environment uses Python 3.9, which does not support it.

Error Details:

File "/project/Logic-RL-main/verl/models/transformers/llama.py", line 17, in <module>
from typing import Optional, List, Union, Tuple, Unpack, Callable
ImportError: cannot import name 'Unpack' from 'typing' (/opt/miniconda3/envs/verl/lib/python3.9/typing.py)

Solution:
To resolve this issue, I added conditional imports to handle different Python versions. For Python versions lower than 3.11, the code now uses a fallback or alternative approach to avoid relying on Unpack.