change schema -> dataset_schema (#442)

# What does this PR do?

- `schema` should not a field w/ pydantic warnings
- change `schema` to `dataset_schema`

<img width="855" alt="image"
src="https://github.com/user-attachments/assets/47cb6bb9-4be0-46a5-8701-24d24e2eaabd">


## Test Plan

```
pytest -v -s -m meta_reference_eval_together_inference_huggingface_datasetio eval/test_eval.py
```


## Before submitting

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

llama_stack/providers/inline/datasetio/localfs/datasetio.py

@@ -60,9 +60,9 @@ class PandasDataframeDataset(BaseDataset):
 
     def _validate_dataset_schema(self, df) -> pandas.DataFrame:
         # note that we will drop any columns in dataset that are not in the schema
-        df = df[self.dataset_def.schema.keys()]
+        df = df[self.dataset_def.dataset_schema.keys()]
         # check all columns in dataset schema are present
-        assert len(df.columns) == len(self.dataset_def.schema)
+        assert len(df.columns) == len(self.dataset_def.dataset_schema)
         # TODO: type checking against column types in dataset schema
         return df