Create a shape_core_utils.py with common code

[gumyr]

There are bits of code that is duplicated in the base topology and geometry layers, downcast being a good example. Within geometry.py one will find:

            downcast_LUT = {
                TopAbs_ShapeEnum.TopAbs_VERTEX: TopoDS.Vertex_s,
                TopAbs_ShapeEnum.TopAbs_EDGE: TopoDS.Edge_s,
                TopAbs_ShapeEnum.TopAbs_WIRE: TopoDS.Wire_s,
                TopAbs_ShapeEnum.TopAbs_FACE: TopoDS.Face_s,
                TopAbs_ShapeEnum.TopAbs_SHELL: TopoDS.Shell_s,
                TopAbs_ShapeEnum.TopAbs_SOLID: TopoDS.Solid_s,
                TopAbs_ShapeEnum.TopAbs_COMPOUND: TopoDS.Compound_s,
            }
            assert other.wrapped is not None
            try:
                f_downcast = downcast_LUT[other.wrapped.ShapeType()]
            except KeyError as exc:
                raise ValueError(f"Unknown object type {other}") from exc

            result: Shape = copy.deepcopy(other, None)  # type: ignore[arg-type]
            result.wrapped = f_downcast(other.wrapped.Moved(self.wrapped))

Note that downcast could be placed in geometry.py as topology imports geometry but this code has to do with Shape objects which only reside in topology. Hence, an independent module that both could import would reduce code duplication.

There may be other bits of code that could go into this new file. Once the typing activities are complete, the output of pylint should be used to highlight all potential code.