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-api/README.md

@@ -0,0 +1,103 @@
+# llama-stack-api
+
+API and Provider specifications for Llama Stack - a lightweight package with protocol definitions and provider specs.
+
+## Overview
+
+`llama-stack-api` is a minimal dependency package that contains:
+
+- **API Protocol Definitions**: Type-safe protocol definitions for all Llama Stack APIs (inference, agents, safety, etc.)
+- **Provider Specifications**: Provider spec definitions for building custom providers
+- **Data Types**: Shared data types and models used across the Llama Stack ecosystem
+- **Type Utilities**: Strong typing utilities and schema validation
+
+## What This Package Does NOT Include
+
+- Server implementation (see `llama-stack` package)
+- Provider implementations (see `llama-stack` package)
+- CLI tools (see `llama-stack` package)
+- Runtime orchestration (see `llama-stack` package)
+
+## Use Cases
+
+This package is designed for:
+
+1. **Third-party Provider Developers**: Build custom providers without depending on the full Llama Stack server
+2. **Client Library Authors**: Use type definitions without server dependencies
+3. **Documentation Generation**: Generate API docs from protocol definitions
+4. **Type Checking**: Validate implementations against the official specs
+
+## Installation
+
+```bash
+pip install llama-stack-api
+```
+
+Or with uv:
+
+```bash
+uv pip install llama-stack-api
+```
+
+## Dependencies
+
+Minimal dependencies:
+- `pydantic>=2.11.9` - For data validation and serialization
+- `jsonschema` - For JSON schema utilities
+
+## Versioning
+
+This package follows semantic versioning independently from the main `llama-stack` package:
+
+- **Patch versions** (0.1.x): Documentation, internal improvements
+- **Minor versions** (0.x.0): New APIs, backward-compatible changes
+- **Major versions** (x.0.0): Breaking changes to existing APIs
+
+Current version: **0.1.0**
+
+## Usage Example
+
+```python
+from llama_stack_api.inference import Inference, ChatCompletionRequest
+from llama_stack_api.providers.datatypes import ProviderSpec, InlineProviderSpec
+from llama_stack_api.datatypes import Api
+
+
+# Use protocol definitions for type checking
+class MyInferenceProvider(Inference):
+    async def chat_completion(self, request: ChatCompletionRequest):
+        # Your implementation
+        pass
+
+
+# Define provider specifications
+my_provider_spec = InlineProviderSpec(
+    api=Api.inference,
+    provider_type="inline::my-provider",
+    pip_packages=["my-dependencies"],
+    module="my_package.providers.inference",
+    config_class="my_package.providers.inference.MyConfig",
+)
+```
+
+## Relationship to llama-stack
+
+The main `llama-stack` package depends on `llama-stack-api` and provides:
+- Full server implementation
+- Built-in provider implementations
+- CLI tools for running and managing stacks
+- Runtime provider resolution and orchestration
+
+## Contributing
+
+See the main [Llama Stack repository](https://github.com/llamastack/llama-stack) for contribution guidelines.
+
+## License
+
+MIT License - see LICENSE file for details.
+
+## Links
+
+- [Main Llama Stack Repository](https://github.com/llamastack/llama-stack)
+- [Documentation](https://llamastack.ai/)
+- [Client Library](https://pypi.org/project/llama-stack-client/)