feat(dataset api): (1.5/n) fix dataset registeration (#1659)

# What does this PR do?

- fix dataset registeration & iterrows
> NOTE: the URL endpoint is changed to datasetio due to flaky path
routing

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan
```
LLAMA_STACK_CONFIG=fireworks pytest -v tests/integration/datasets/test_datasets.py
```
<img width="854" alt="image"
src="https://github.com/user-attachments/assets/0168b352-1c5a-48d1-8e9a-93141d418e54"
/>


[//]: # (## Documentation)

tests/integration/datasets/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/integration/datasets/test_dataset.csv

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+input_query,generated_answer,expected_answer,chat_completion_input
+What is the capital of France?,London,Paris,"[{""role"": ""user"", ""content"": ""What is the capital of France?""}]"
+Who is the CEO of Meta?,Mark Zuckerberg,Mark Zuckerberg,"[{""role"": ""user"", ""content"": ""Who is the CEO of Meta?""}]"
+What is the largest planet in our solar system?,Jupiter,Jupiter,"[{""role"": ""user"", ""content"": ""What is the largest planet in our solar system?""}]"
+What is the smallest country in the world?,China,Vatican City,"[{""role"": ""user"", ""content"": ""What is the smallest country in the world?""}]"
+What is the currency of Japan?,Yen,Yen,"[{""role"": ""user"", ""content"": ""What is the currency of Japan?""}]"

tests/integration/datasets/test_datasets.py

@@ -0,0 +1,95 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+
+import base64
+import mimetypes
+import os
+
+import pytest
+
+# How to run this test:
+#
+# LLAMA_STACK_CONFIG="template-name" pytest -v tests/integration/datasets
+
+
+def data_url_from_file(file_path: str) -> str:
+    if not os.path.exists(file_path):
+        raise FileNotFoundError(f"File not found: {file_path}")
+
+    with open(file_path, "rb") as file:
+        file_content = file.read()
+
+    base64_content = base64.b64encode(file_content).decode("utf-8")
+    mime_type, _ = mimetypes.guess_type(file_path)
+
+    data_url = f"data:{mime_type};base64,{base64_content}"
+
+    return data_url
+
+
+@pytest.mark.parametrize(
+    "purpose, source, provider_id, limit",
+    [
+        (
+            "eval/messages-answer",
+            {
+                "type": "uri",
+                "uri": "huggingface://datasets/llamastack/simpleqa?split=train",
+            },
+            "huggingface",
+            10,
+        ),
+        (
+            "eval/messages-answer",
+            {
+                "type": "rows",
+                "rows": [
+                    {
+                        "messages": [{"role": "user", "content": "Hello, world!"}],
+                        "answer": "Hello, world!",
+                    },
+                    {
+                        "messages": [
+                            {
+                                "role": "user",
+                                "content": "What is the capital of France?",
+                            }
+                        ],
+                        "answer": "Paris",
+                    },
+                ],
+            },
+            "localfs",
+            2,
+        ),
+        (
+            "eval/messages-answer",
+            {
+                "type": "uri",
+                "uri": data_url_from_file(os.path.join(os.path.dirname(__file__), "test_dataset.csv")),
+            },
+            "localfs",
+            5,
+        ),
+    ],
+)
+def test_register_and_iterrows(llama_stack_client, purpose, source, provider_id, limit):
+    dataset = llama_stack_client.datasets.register(
+        purpose=purpose,
+        source=source,
+    )
+    assert dataset.identifier is not None
+    assert dataset.provider_id == provider_id
+    iterrow_response = llama_stack_client.datasets.iterrows(dataset.identifier, limit=limit)
+    assert len(iterrow_response.data) == limit
+
+    dataset_list = llama_stack_client.datasets.list()
+    assert dataset.identifier in [d.identifier for d in dataset_list]
+
+    llama_stack_client.datasets.unregister(dataset.identifier)
+    dataset_list = llama_stack_client.datasets.list()
+    assert dataset.identifier not in [d.identifier for d in dataset_list]

tests/integration/datasets/test_rag_dataset.csv

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+input_query,context,generated_answer,expected_answer
+What is the capital of France?,"France is a country in Western Europe with a population of about 67 million people. Its capital city has been a major European cultural center since the 17th century and is known for landmarks like the Eiffel Tower and the Louvre Museum.",London,Paris
+Who is the CEO of Meta?,"Meta Platforms, formerly known as Facebook, is one of the world's largest technology companies. Founded by Mark Zuckerberg in 2004, the company has expanded to include platforms like Instagram, WhatsApp, and virtual reality technologies.",Mark Zuckerberg,Mark Zuckerberg
+What is the largest planet in our solar system?,"The solar system consists of eight planets orbiting around the Sun. These planets, in order from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Gas giants are significantly larger than terrestrial planets.",Jupiter,Jupiter
+What is the smallest country in the world?,"Independent city-states and micronations are among the world's smallest sovereign territories. Some notable examples include Monaco, San Marino, and Vatican City, which is an enclave within Rome, Italy.",China,Vatican City
+What is the currency of Japan?,"Japan is an island country in East Asia with a rich cultural heritage and one of the world's largest economies. Its financial system has been established since the Meiji period, with its modern currency being introduced in 1871.",Yen,Yen