chore(package): migrate to src/ layout (#3920)

Migrates package structure to src/ layout following Python packaging
best practices.

All code moved from `llama_stack/` to `src/llama_stack/`. Public API
unchanged - imports remain `import llama_stack.*`.

Updated build configs, pre-commit hooks, scripts, and GitHub workflows
accordingly. All hooks pass, package builds cleanly.

**Developer note**: Reinstall after pulling: `pip install -e .`

src/llama_stack/apis/providers/providers.py

@@ -0,0 +1,69 @@
+# 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 Any, Protocol, runtime_checkable
+
+from pydantic import BaseModel
+
+from llama_stack.apis.version import LLAMA_STACK_API_V1
+from llama_stack.providers.datatypes import HealthResponse
+from llama_stack.schema_utils import json_schema_type, webmethod
+
+
+@json_schema_type
+class ProviderInfo(BaseModel):
+    """Information about a registered provider including its configuration and health status.
+
+    :param api: The API name this provider implements
+    :param provider_id: Unique identifier for the provider
+    :param provider_type: The type of provider implementation
+    :param config: Configuration parameters for the provider
+    :param health: Current health status of the provider
+    """
+
+    api: str
+    provider_id: str
+    provider_type: str
+    config: dict[str, Any]
+    health: HealthResponse
+
+
+class ListProvidersResponse(BaseModel):
+    """Response containing a list of all available providers.
+
+    :param data: List of provider information objects
+    """
+
+    data: list[ProviderInfo]
+
+
+@runtime_checkable
+class Providers(Protocol):
+    """Providers
+
+    Providers API for inspecting, listing, and modifying providers and their configurations.
+    """
+
+    @webmethod(route="/providers", method="GET", level=LLAMA_STACK_API_V1)
+    async def list_providers(self) -> ListProvidersResponse:
+        """List providers.
+
+        List all available providers.
+
+        :returns: A ListProvidersResponse containing information about all providers.
+        """
+        ...
+
+    @webmethod(route="/providers/{provider_id}", method="GET", level=LLAMA_STACK_API_V1)
+    async def inspect_provider(self, provider_id: str) -> ProviderInfo:
+        """Get provider.
+
+        Get detailed information about a specific provider.
+
+        :param provider_id: The ID of the provider to inspect.
+        :returns: A ProviderInfo object containing the provider's details.
+        """
+        ...