test(xrayeye): keep the ellipse-ROI test items in a module-lifetime QGraphicsScene

Unparented pyqtgraph ROIs could be garbage-collected while the next ROI was being
built, which crashed PySide6 in CI with --random-order (segfault in
GraphicsObject.itemChange during garbage collection). Test logic unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TNtKEk4jAyjebMDQFwRHJQ

tests/tests_bec_widgets/test_x_ray_eye_ellipse_roi.py

@@ -27,6 +27,22 @@ def _qapp():
     return pg.mkQApp()
 
 
+# All test ROIs go into one scene that lives for the whole module: Qt then owns the items, and the
+# Python garbage collector cannot delete an unparented ROI while the next one is being built (that
+# crashed PySide6 / pyqtgraph in CI with --random-order: "Fatal Python error: Segmentation fault" in
+# GraphicsObject.itemChange during garbage collection).
+_SCENE = None
+
+
+@pytest.fixture(autouse=True, scope="module")
+def _scene(_qapp):
+    global _SCENE
+    _SCENE = pg.QtWidgets.QGraphicsScene()
+    yield _SCENE
+    _SCENE.clear()
+    _SCENE = None
+
+
 class _FakeEllipticalROI(pg.EllipseROI):
     """pg ellipse standing in for bec_widgets' EllipticalROI in isinstance checks."""
 
@@ -39,6 +55,7 @@ def _patch_roi_class():
 
 def _roi(pos=(10.0, 20.0), size=(40.0, 20.0), angle=0.0):
     roi = _FakeEllipticalROI(pos, size, angle=angle)
+    _SCENE.addItem(roi)
     return roi