Check validity of shapely geometries in `ShapesModel.parse()`

In tests/conftest.py the second multipolygon of the multipoly object is invalid, i.e.

    multipoly = GeoDataFrame(
        {
            "geometry": [
                MultiPolygon(
                    [
                        Polygon(((0, 0), (0, 1), (1, 1), (1, 0))),
                        Polygon(((0, 0), (0, -1), (-1, -1), (-1, 0))),
                    ]
                ),
                MultiPolygon(
                    [
                        Polygon(((0, 0), (0, 1), (1, 10))),
                        Polygon(((0, 0), (0, 1), (1, 1))),
                        Polygon(((0, 0), (0, 1), (1, 1), (1, 0), (1, 0))),
                    ]
                ),
            ]
        }

leads to multipoly.is_valid having False at the second entry.

This may cause subtle problems when operating on those objects; for instance this query fails:

    indices = polygons.geometry.intersects(bounding_box_non_axes_aligned)

A solution is to prevent such geometries to pass the validation step when invoking parse() and validate() in ShapesModel.

Start with ShapesModel.parse() and validate(), then inspect the invalid multipoly fixture in tests/conftest.py. Reproduce the failing geometry operation using polygons.geometry.intersects(bounding_box_non_axes_aligned). Done means invalid shapely geometries are rejected during ShapesModel parsing and validation.