Fix: Use correct local path when loading base model from s3

[fadebek]

Previously, when loading a base model from s3:

--source s3 --model-id s3://bucket/model

The model would be downloaded to the cache path /data/models--model. However, when the base model is first loaded, it tried to search the incorrect path /data/models--s3:----bucket--model which causes an error since the directory doesnt exist.