Add metapackage metadata stub to restore flit builds (#1043)

python/agent_framework_meta/__init__.py

@@ -0,0 +1,31 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from importlib import metadata as _metadata
+from pathlib import Path as _Path
+from typing import Any, cast
+
+try:
+    import tomllib as _toml  # type: ignore # Python 3.11+
+except ModuleNotFoundError:  # Python 3.10
+    import tomli as _toml  # type: ignore
+
+
+def _load_pyproject() -> dict[str, Any]:
+    pyproject = (_Path(__file__).resolve().parents[1] / "pyproject.toml").read_text("utf-8")
+    return cast(dict[str, Any], _toml.loads(pyproject))  # type: ignore
+
+
+def _version() -> str:
+    try:
+        return _metadata.version("agent-framework")
+    except _metadata.PackageNotFoundError as ex:
+        data = _load_pyproject()
+        project = cast(dict[str, Any], data.get("project", {}))
+        version = project.get("version")
+        if isinstance(version, str):
+            return version
+        raise RuntimeError("pyproject.toml missing project.version") from ex
+
+
+__version__ = _version()
+__all__ = ["__version__"]