add NVIDIA NIM inference adapter (#355)

# What does this PR do?

this PR adds a basic inference adapter to NVIDIA NIMs

what it does -
 - chat completion api
   - tool calls
   - streaming
   - structured output
   - logprobs
 - support hosted NIM on integrate.api.nvidia.com
 - support downloaded NIM containers

what it does not do -
 - completion api
 - embedding api
 - vision models
 - builtin tools
 - have certainty that sampling strategies are correct

## Feature/Issue validation/testing/test plan

`pytest -s -v --providers inference=nvidia
llama_stack/providers/tests/inference/ --env NVIDIA_API_KEY=...`

all tests should pass. there are pydantic v1 warnings.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Did you read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes?
- [x] Did you write any new necessary tests?

Thanks for contributing 🎉!

llama_stack/providers/remote/inference/nvidia/utils.py

@@ -0,0 +1,54 @@
+# 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.
+
+from typing import Tuple
+
+import httpx
+
+from . import NVIDIAConfig
+
+
+def _is_nvidia_hosted(config: NVIDIAConfig) -> bool:
+    return "integrate.api.nvidia.com" in config.url
+
+
+async def _get_health(url: str) -> Tuple[bool, bool]:
+    """
+    Query {url}/v1/health/{live,ready} to check if the server is running and ready
+
+    Args:
+        url (str): URL of the server
+
+    Returns:
+        Tuple[bool, bool]: (is_live, is_ready)
+    """
+    async with httpx.AsyncClient() as client:
+        live = await client.get(f"{url}/v1/health/live")
+        ready = await client.get(f"{url}/v1/health/ready")
+        return live.status_code == 200, ready.status_code == 200
+
+
+async def check_health(config: NVIDIAConfig) -> None:
+    """
+    Check if the server is running and ready
+
+    Args:
+        url (str): URL of the server
+
+    Raises:
+        RuntimeError: If the server is not running or ready
+    """
+    if not _is_nvidia_hosted(config):
+        print("Checking NVIDIA NIM health...")
+        try:
+            is_live, is_ready = await _get_health(config.url)
+            if not is_live:
+                raise ConnectionError("NVIDIA NIM is not running")
+            if not is_ready:
+                raise ConnectionError("NVIDIA NIM is not ready")
+            # TODO(mf): should we wait for the server to be ready?
+        except httpx.ConnectError as e:
+            raise ConnectionError(f"Failed to connect to NVIDIA NIM: {e}") from e