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>

docs/openapi_generator/pyopenapi/utility.py

@@ -11,8 +11,7 @@ from pathlib import Path
 from typing import Any, List, Optional, TextIO, Union, get_type_hints, get_origin, get_args
 
 from pydantic import BaseModel
-from llama_stack.strong_typing.schema import object_to_json, StrictJsonType
-from llama_stack.strong_typing.inspection import is_unwrapped_body_param
+from llama_stack_api import StrictJsonType, is_unwrapped_body_param, object_to_json
 from llama_stack.core.resolver import api_protocol_map
 
 from .generator import Generator
@@ -165,12 +164,12 @@ def _validate_api_delete_method_returns_none(method) -> str | None:
         return "has no return type annotation"
 
     return_type = hints['return']
-    
+
     # Allow OpenAI endpoints to return response objects since they follow OpenAI specification
     method_name = getattr(method, '__name__', '')
     if method_name.__contains__('openai_'):
         return None
-    
+
     if return_type is not None and return_type is not type(None):
         return "does not return None where None is mandatory"