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>

src/llama_stack/core/server/auth_providers.py

@@ -11,9 +11,9 @@ from urllib.parse import parse_qs, urljoin, urlparse
 
 import httpx
 import jwt
+from llama_stack_api import TokenValidationError
 from pydantic import BaseModel, Field
 
-from llama_stack.apis.common.errors import TokenValidationError
 from llama_stack.core.datatypes import (
     AuthenticationConfig,
     CustomAuthConfig,

src/llama_stack/core/server/routes.py

@@ -10,11 +10,10 @@ from collections.abc import Callable
 from typing import Any
 
 from aiohttp import hdrs
+from llama_stack_api import Api, ExternalApiSpec, WebMethod
 from starlette.routing import Route
 
-from llama_stack.apis.datatypes import Api, ExternalApiSpec
 from llama_stack.core.resolver import api_protocol_map
-from llama_stack.schema_utils import WebMethod
 
 EndpointFunc = Callable[..., Any]
 PathParams = dict[str, str]

src/llama_stack/core/server/server.py

@@ -28,11 +28,10 @@ from fastapi import Path as FastapiPath
 from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse, StreamingResponse
+from llama_stack_api import Api, ConflictError, PaginatedResponse, ResourceNotFoundError
 from openai import BadRequestError
 from pydantic import BaseModel, ValidationError
 
-from llama_stack.apis.common.errors import ConflictError, ResourceNotFoundError
-from llama_stack.apis.common.responses import PaginatedResponse
 from llama_stack.core.access_control.access_control import AccessDeniedError
 from llama_stack.core.datatypes import (
     AuthenticationRequiredError,
@@ -58,7 +57,6 @@ from llama_stack.core.utils.config import redact_sensitive_fields
 from llama_stack.core.utils.config_resolution import Mode, resolve_config_or_distro
 from llama_stack.core.utils.context import preserve_contexts_async_generator
 from llama_stack.log import LoggingConfig, get_logger, setup_logging
-from llama_stack.providers.datatypes import Api
 
 from .auth import AuthenticationMiddleware
 from .quota import QuotaMiddleware