Add conftest.py to guard agent_framework imports in CI unit tests

In some CI environments (Linux Python 3.12) agent_framework loads but
its top-level namespace is missing RawAgent/MCPStreamableHTTPTool due to
a partial circular-import during pytest collection.  The new conftest.py
is loaded by pytest before test files in this directory tree are imported,
and adds MagicMock stubs for any absent names so the module-level
`from agent_framework import ...` in the production service succeeds.

Author: biswapm

tests/tooling/extensions/agentframework/conftest.py

@@ -0,0 +1,25 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+"""Conftest for Agent Framework tooling extension unit tests.
+
+Ensures that ``agent_framework`` exports required by the production module are
+available in the test environment.  In some CI configurations the package is
+importable but its internal initialisation leaves certain names absent from the
+top-level namespace (e.g. a partial circular-import during collection).  We
+patch the stubs in at conftest *module load* time — which pytest guarantees
+happens before it imports any test file in this directory tree.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+# fmt: off
+import agent_framework as _af  # noqa: E402
+
+_REQUIRED = ("RawAgent", "MCPStreamableHTTPTool", "Message", "HistoryProvider")
+for _name in _REQUIRED:
+    if not hasattr(_af, _name):
+        setattr(_af, _name, MagicMock(name=f"agent_framework.{_name}"))
+# fmt: on