fix: finish conversion to StrEnum (#2514)

# What does this PR do?

We still had a few enum declared to behave like string as well as enum.
Let's use StrEnum for those.

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/apis/datasets/datasets.py

@@ -4,7 +4,7 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from enum import Enum
+from enum import Enum, StrEnum
 from typing import Annotated, Any, Literal, Protocol
 
 from pydantic import BaseModel, Field
@@ -13,7 +13,7 @@ from llama_stack.apis.resource import Resource, ResourceType
 from llama_stack.schema_utils import json_schema_type, register_schema, webmethod
 
 
-class DatasetPurpose(str, Enum):
+class DatasetPurpose(StrEnum):
     """
     Purpose of the dataset. Each purpose has a required input data schema.
 

llama_stack/apis/files/files.py

@@ -4,7 +4,7 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from enum import Enum
+from enum import StrEnum
 from typing import Annotated, Literal, Protocol, runtime_checkable
 
 from fastapi import File, Form, Response, UploadFile
@@ -16,7 +16,7 @@ from llama_stack.schema_utils import json_schema_type, webmethod
 
 
 # OpenAI Files API Models
-class OpenAIFilePurpose(str, Enum):
+class OpenAIFilePurpose(StrEnum):
     """
     Valid purpose values for OpenAI Files API.
     """

llama_stack/apis/models/models.py

@@ -4,7 +4,7 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from enum import Enum
+from enum import StrEnum
 from typing import Any, Literal, Protocol, runtime_checkable
 
 from pydantic import BaseModel, ConfigDict, Field
@@ -22,7 +22,7 @@ class CommonModelFields(BaseModel):
 
 
 @json_schema_type
-class ModelType(str, Enum):
+class ModelType(StrEnum):
     llm = "llm"
     embedding = "embedding"