feat: Add NVIDIA NeMo datastore (#1852)

# What does this PR do?
Implemetation of NeMO Datastore register, unregister API.

Open Issues: 
- provider_id gets set to `localfs` in client.datasets.register() as it
is specified in routing_tables.py: DatasetsRoutingTable
see: #1860

Currently I have passed `"provider_id":"nvidia"` in metadata and have
parsed that in `DatasetsRoutingTable`
(Not the best approach, but just a quick workaround to make it work for
now.)

## Test Plan
- Unit test cases: `pytest
tests/unit/providers/nvidia/test_datastore.py`
```bash
========================================================== test session starts ===========================================================
platform linux -- Python 3.10.0, pytest-8.3.5, pluggy-1.5.0
rootdir: /home/ubuntu/llama-stack
configfile: pyproject.toml
plugins: anyio-4.9.0, asyncio-0.26.0, nbval-0.11.0, metadata-3.1.1, html-4.1.1, cov-6.1.0
asyncio: mode=strict, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 2 items                                                                                                                        

tests/unit/providers/nvidia/test_datastore.py ..                                                                                   [100%]

============================================================ warnings summary ============================================================

====================================================== 2 passed, 1 warning in 0.84s ======================================================
```

cc: @dglogo, @mattf, @yanxi0830

tests/unit/providers/nvidia/test_datastore.py

@@ -0,0 +1,138 @@
+# 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 os
+import unittest
+from unittest.mock import patch
+
+import pytest
+
+from llama_stack.apis.datasets import Dataset, DatasetPurpose, URIDataSource
+from llama_stack.providers.remote.datasetio.nvidia.config import NvidiaDatasetIOConfig
+from llama_stack.providers.remote.datasetio.nvidia.datasetio import NvidiaDatasetIOAdapter
+
+
+class TestNvidiaDatastore(unittest.TestCase):
+    def setUp(self):
+        os.environ["NVIDIA_DATASETS_URL"] = "http://nemo.test/datasets"
+
+        config = NvidiaDatasetIOConfig(
+            datasets_url=os.environ["NVIDIA_DATASETS_URL"], dataset_namespace="default", project_id="default"
+        )
+        self.adapter = NvidiaDatasetIOAdapter(config)
+        self.make_request_patcher = patch(
+            "llama_stack.providers.remote.datasetio.nvidia.datasetio.NvidiaDatasetIOAdapter._make_request"
+        )
+        self.mock_make_request = self.make_request_patcher.start()
+
+    def tearDown(self):
+        self.make_request_patcher.stop()
+
+    @pytest.fixture(autouse=True)
+    def inject_fixtures(self, run_async):
+        self.run_async = run_async
+
+    def _assert_request(self, mock_call, expected_method, expected_path, expected_json=None):
+        """Helper method to verify request details in mock calls."""
+        call_args = mock_call.call_args
+
+        assert call_args[0][0] == expected_method
+        assert call_args[0][1] == expected_path
+
+        if expected_json:
+            for key, value in expected_json.items():
+                assert call_args[1]["json"][key] == value
+
+    def test_register_dataset(self):
+        self.mock_make_request.return_value = {
+            "id": "dataset-123456",
+            "name": "test-dataset",
+            "namespace": "default",
+        }
+
+        dataset_def = Dataset(
+            identifier="test-dataset",
+            type="dataset",
+            provider_resource_id="",
+            provider_id="",
+            purpose=DatasetPurpose.post_training_messages,
+            source=URIDataSource(uri="https://example.com/data.jsonl"),
+            metadata={"provider_id": "nvidia", "format": "jsonl", "description": "Test dataset description"},
+        )
+
+        self.run_async(self.adapter.register_dataset(dataset_def))
+
+        self.mock_make_request.assert_called_once()
+        self._assert_request(
+            self.mock_make_request,
+            "POST",
+            "/v1/datasets",
+            expected_json={
+                "name": "test-dataset",
+                "namespace": "default",
+                "files_url": "https://example.com/data.jsonl",
+                "project": "default",
+                "format": "jsonl",
+                "description": "Test dataset description",
+            },
+        )
+
+    def test_unregister_dataset(self):
+        self.mock_make_request.return_value = {
+            "message": "Resource deleted successfully.",
+            "id": "dataset-81RSQp7FKX3rdBtKvF9Skn",
+            "deleted_at": None,
+        }
+        dataset_id = "test-dataset"
+
+        self.run_async(self.adapter.unregister_dataset(dataset_id))
+
+        self.mock_make_request.assert_called_once()
+        self._assert_request(self.mock_make_request, "DELETE", "/v1/datasets/default/test-dataset")
+
+    def test_register_dataset_with_custom_namespace_project(self):
+        custom_config = NvidiaDatasetIOConfig(
+            datasets_url=os.environ["NVIDIA_DATASETS_URL"],
+            dataset_namespace="custom-namespace",
+            project_id="custom-project",
+        )
+        custom_adapter = NvidiaDatasetIOAdapter(custom_config)
+
+        self.mock_make_request.return_value = {
+            "id": "dataset-123456",
+            "name": "test-dataset",
+            "namespace": "custom-namespace",
+        }
+
+        dataset_def = Dataset(
+            identifier="test-dataset",
+            type="dataset",
+            provider_resource_id="",
+            provider_id="",
+            purpose=DatasetPurpose.post_training_messages,
+            source=URIDataSource(uri="https://example.com/data.jsonl"),
+            metadata={"format": "jsonl"},
+        )
+
+        self.run_async(custom_adapter.register_dataset(dataset_def))
+
+        self.mock_make_request.assert_called_once()
+        self._assert_request(
+            self.mock_make_request,
+            "POST",
+            "/v1/datasets",
+            expected_json={
+                "name": "test-dataset",
+                "namespace": "custom-namespace",
+                "files_url": "https://example.com/data.jsonl",
+                "project": "custom-project",
+                "format": "jsonl",
+            },
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()