remove pydantic namespace warnings using model_config (#470)

# What does this PR do?

remove another model_ pydantic namespace warning and convert old-style
'class Config' to new-style 'model_config' workaround.

also a whitespace change to get past -


flake8...................................................................Failed
llama_stack/cli/download.py:296:85: E226 missing whitespace around
arithmetic operator
llama_stack/cli/download.py:297:54: E226 missing whitespace around
arithmetic operator


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Ran pre-commit to handle lint / formatting issues.
- [x] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [x] Wrote necessary unit or integration tests.

llama_stack/apis/models/models.py

@@ -31,6 +31,8 @@ class Model(CommonModelFields, Resource):
     def provider_model_id(self) -> str:
         return self.provider_resource_id
 
+    model_config = ConfigDict(protected_namespaces=())
+
 
 class ModelInput(CommonModelFields):
     model_id: str