FIX: correctly restore the size of unpickled figures with hi-dpi

The issue is that we reset the dpi but did not re-compute any of the
bounding boxes derived from the dpi leading to the initial redraw events
to use the wrong physical size on the screen.

Closes matplotlib#27224

Author: tacaswell

lib/matplotlib/figure.py

@@ -3321,8 +3321,9 @@ def __setstate__(self, state):
         self.__dict__ = state
 
         # re-initialise some of the unstored state information
-        FigureCanvasBase(self)  # Set self.canvas.
-
+        self._set_base_canvas()
+        # force the bounding boxes to respect current dpi
+        self.dpi_scale_trans.clear().scale(self._dpi)
         if restore_to_pylab:
             # lazy import to avoid circularity
             import matplotlib.pyplot as plt

lib/matplotlib/tests/test_figure.py

@@ -1688,6 +1688,9 @@ def test_unpickle_with_device_pixel_ratio():
     assert fig.dpi == 42*7
     fig2 = pickle.loads(pickle.dumps(fig))
     assert fig2.dpi == 42
+    assert all(
+        [orig / 7 == restore for orig, restore in zip(fig.bbox.max, fig2.bbox.max)]
+    )
 
 
 def test_gridspec_no_mutate_input():