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/providers/remote/inference/anthropic/__init__.py

@@ -0,0 +1,15 @@
+# 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 .config import AnthropicConfig
+
+
+async def get_adapter_impl(config: AnthropicConfig, _deps):
+    from .anthropic import AnthropicInferenceAdapter
+
+    impl = AnthropicInferenceAdapter(config=config)
+    await impl.initialize()
+    return impl

src/llama_stack/providers/remote/inference/anthropic/anthropic.py

@@ -0,0 +1,36 @@
+# 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 collections.abc import Iterable
+
+from anthropic import AsyncAnthropic
+
+from llama_stack.providers.utils.inference.openai_mixin import OpenAIMixin
+
+from .config import AnthropicConfig
+
+
+class AnthropicInferenceAdapter(OpenAIMixin):
+    config: AnthropicConfig
+
+    provider_data_api_key_field: str = "anthropic_api_key"
+    # source: https://docs.claude.com/en/docs/build-with-claude/embeddings
+    # TODO: add support for voyageai, which is where these models are hosted
+    # embedding_model_metadata = {
+    #     "voyage-3-large": {"embedding_dimension": 1024, "context_length": 32000},  # supports dimensions 256, 512, 1024, 2048
+    #     "voyage-3.5": {"embedding_dimension": 1024, "context_length": 32000},  # supports dimensions 256, 512, 1024, 2048
+    #     "voyage-3.5-lite": {"embedding_dimension": 1024, "context_length": 32000},  # supports dimensions 256, 512, 1024, 2048
+    #     "voyage-code-3": {"embedding_dimension": 1024, "context_length": 32000},  # supports dimensions 256, 512, 1024, 2048
+    #     "voyage-finance-2": {"embedding_dimension": 1024, "context_length": 32000},
+    #     "voyage-law-2": {"embedding_dimension": 1024, "context_length": 16000},
+    #     "voyage-multimodal-3": {"embedding_dimension": 1024, "context_length": 32000},
+    # }
+
+    def get_base_url(self):
+        return "https://api.anthropic.com/v1"
+
+    async def list_provider_model_ids(self) -> Iterable[str]:
+        return [m.id async for m in AsyncAnthropic(api_key=self.get_api_key()).models.list()]

src/llama_stack/providers/remote/inference/anthropic/config.py

@@ -0,0 +1,28 @@
+# 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
+
+from pydantic import BaseModel, Field
+
+from llama_stack.providers.utils.inference.model_registry import RemoteInferenceProviderConfig
+from llama_stack.schema_utils import json_schema_type
+
+
+class AnthropicProviderDataValidator(BaseModel):
+    anthropic_api_key: str | None = Field(
+        default=None,
+        description="API key for Anthropic models",
+    )
+
+
+@json_schema_type
+class AnthropicConfig(RemoteInferenceProviderConfig):
+    @classmethod
+    def sample_run_config(cls, api_key: str = "${env.ANTHROPIC_API_KEY:=}", **kwargs) -> dict[str, Any]:
+        return {
+            "api_key": api_key,
+        }