feat: split API and provider specs into separate llama-stack-api pkg (#3895)

# What does this PR do?

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


see: https://github.com/llamastack/llama-stack/pull/2978 and
https://github.com/llamastack/llama-stack/pull/2978#issuecomment-3145115942

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.*
- Configured local editable install for development workflow
- Updated linting and type-checking configuration for both packages

Next Steps

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


Pre-cursor PRs to this one:

- #4093 
- #3954 
- #4064 

These PRs moved key pieces _out_ of the Api pkg, limiting the scope of
change here.


relates to #3237 

## Test Plan

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

---------

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

scripts/provider_codegen.py

@@ -22,7 +22,7 @@ def get_api_docstring(api_name: str) -> str | None:
     """Extract docstring from the API protocol class."""
     try:
         # Import the API module dynamically
-        api_module = __import__(f"llama_stack.apis.{api_name}", fromlist=[api_name.title()])
+        api_module = __import__(f"llama_stack_api.{api_name}", fromlist=[api_name.title()])
 
         # Get the main protocol class (usually capitalized API name)
         protocol_class_name = api_name.title()
@@ -83,8 +83,9 @@ def get_config_class_info(config_class_path: str) -> dict[str, Any]:
                 # this string replace is ridiculous
                 field_type = field_type.replace("typing.", "").replace("Optional[", "").replace("]", "")
                 field_type = field_type.replace("Annotated[", "").replace("FieldInfo(", "").replace(")", "")
-                field_type = field_type.replace("llama_stack.apis.inference.inference.", "")
+                field_type = field_type.replace("llama_stack_api.inference.", "")
                 field_type = field_type.replace("llama_stack.providers.", "")
+                field_type = field_type.replace("llama_stack_api.datatypes.", "")
 
                 default_value = field.default
                 if field.default_factory is not None: