Fix hole positions offset by burn in FingerHoleEdge

When rendering the FingerHoleEdge, the current position would be
corrected for burn (e.g. it would be on the center of the laser path,
rather than the actual edge of the final part). However, the FingerHoles
class (or actually the rectangularHole method called by it) that draws
the actual holes already corrects for burn, which caused the hole
position to be offset by the burn value.

This offset was particularly problematic when making a sliding lid,
since the holes would not align perfectly with the lid, making it hard
to close the lid. With this change, the sliding slots in the side walls
and the holes in the back wall align perfectly (though only when the lid
settings have zero play, which is a separate problem).

This commit fixes FingerHoleEdge (and its subclass LidHoleEdge), but
there might be other users of the FingerHole class (usually indirectly
through boxes.fingerHolesAt) that still have the same problem.

boxes/edges.py

@@ -716,7 +716,7 @@ class FingerHoleEdge(BaseEdge):
         dist = self.fingerHoles.settings.edge_width
         with self.saved_context():
             self.fingerHoles(
-                0, dist + self.settings.thickness / 2, length, 0,
+                0, self.burn + dist + self.settings.thickness / 2, length, 0,
                 bedBolts=bedBolts, bedBoltSettings=bedBoltSettings)
         self.edge(length, tabs=2)