openapi support

[moldis]

OpenAPI support within the dazl-client library:

Added auto-generated support for OpenAPI clients (JSON-based) using the openapi-python-client library.

Introduced new Makefile targets:

download-openapi — downloads the Swagger definition from the Splice node and stores it in the cache folder.
generate-api — generates Python bindings (models and methods), stores the generated classes in python/dazl/__gen_api/openapi, and applies header updates and method fixes for compatibility.
clean-openapi — removes the downloaded Swagger definition.

• Exported API methods via python/dazl/api/__init__.py, making them available for developers to import, and added AuthenticatedClient.
• Updated the sandbox launcher to support JSON API.
• Added basic unit test coverage for the generated API methods.

Example of usage in actual code:

timeout = httpx.Timeout(10.0, connect=5.0) async with AuthenticatedClient( base_url=sandbox_v3.url, token="test-token", timeout=timeout, ) as client: response = await get_v2_parties.asyncio(client=client) assert isinstance(response, ListKnownPartiesResponse) 

Ignore files in python/dazl/_gen_api/openapi, since they autogenerate