feat: split API and provider specs into separate llama-stack-api pkg

Extract API definitions, models, and provider specifications into a
standalone llama-stack-api package that can be published to PyPI
independently of the main llama-stack server.

Motivation

External providers currently import from llama-stack, which overrides
the installed version and causes dependency conflicts. This separation
allows external providers to:

- Install only the type definitions they need without server dependencies
- Avoid version conflicts with the installed llama-stack package
- Be versioned and released independently

This enables us to re-enable external provider module tests that were
previously blocked by these import conflicts.

Changes

- Created llama-stack-api package with minimal dependencies (pydantic, jsonschema)
- Moved APIs, providers datatypes, strong_typing, and schema_utils
- Updated all imports from llama_stack.* to llama_stack_api.*
- Preserved git history using git mv for moved files
- Configured local editable install for development workflow
- Updated linting and type-checking configuration for both packages
- Rebased on top of upstream src/ layout changes

Testing

Package builds successfully and can be imported independently.
All pre-commit hooks pass with expected exclusions maintained.

Next Steps

- Publish llama-stack-api to PyPI
- Update external provider dependencies
- Re-enable external provider module tests

Signed-off-by: Charlie Doern <cdoern@redhat.com>

tests/unit/registry/test_registry.py

@@ -6,9 +6,9 @@
 
 
 import pytest
+from llama_stack_api.apis.inference import Model
+from llama_stack_api.apis.vector_stores import VectorStore
 
-from llama_stack.apis.inference import Model
-from llama_stack.apis.vector_stores import VectorStore
 from llama_stack.core.datatypes import VectorStoreWithOwner
 from llama_stack.core.storage.datatypes import KVStoreReference, SqliteKVStoreConfig
 from llama_stack.core.store.registry import (
@@ -304,7 +304,8 @@ async def test_double_registration_different_objects(disk_dist_registry):
 
 async def test_double_registration_with_cache(cached_disk_dist_registry):
     """Test double registration behavior with caching enabled."""
-    from llama_stack.apis.models import ModelType
+    from llama_stack_api.apis.models import ModelType
+
     from llama_stack.core.datatypes import ModelWithOwner
 
     model1 = ModelWithOwner(