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/eval/meta_reference/eval.py

@@ -58,7 +58,7 @@ class MetaReferenceEvalImpl(Eval, EvalTasksProtocolPrivate):
 
     async def validate_eval_input_dataset_schema(self, dataset_id: str) -> None:
         dataset_def = await self.datasets_api.get_dataset(dataset_id=dataset_id)
-        if not dataset_def.schema or len(dataset_def.schema) == 0:
+        if not dataset_def.dataset_schema or len(dataset_def.dataset_schema) == 0:
             raise ValueError(f"Dataset {dataset_id} does not have a schema defined.")
 
         expected_schemas = [
@@ -74,7 +74,7 @@ class MetaReferenceEvalImpl(Eval, EvalTasksProtocolPrivate):
             },
         ]
 
-        if dataset_def.schema not in expected_schemas:
+        if dataset_def.dataset_schema not in expected_schemas:
             raise ValueError(
                 f"Dataset {dataset_id} does not have a correct input schema in {expected_schemas}"
             )