Update Paths To Use `os.path.join`

[AryaanSheth]

Update the file paths in project to use os.path.join over raw string literals for paths.

I found raw string file paths located in the following files:

• weights/convert_safetensor_to_pt.py
• utils.py
• omniparser.py
• gradio_demo.py

This change will improve the readability of the code and reduce the likelihood of errors that are caused my raw string paths.