GeometrySnapper.snapToSelf can produce an incorrect polygonal result when multiple target vertices are within the snap tolerance

JTS version
JTS 1.20.0

GeometrySnapper.snapToSelf produces an unexpected result for the following valid MultiPolygon when using a snap tolerance of 0.005.

With cleanResult = false, self-snapping can create invalid/local self-intersecting polygon topology.
With cleanResult = true, the subsequent cleanup can then produce a substantially different polygonal result.

`import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.io.WKTReader;
import org.locationtech.jts.operation.overlay.snap.GeometrySnapper;

public class SnapToSelfReproducer {

private static final String WKT =
        "MULTIPOLYGON (((641868.09 411913.34, " +
                "641884.99 411907.36, " +
                "641917.6671767097 411902.33050147054, " +
                "641901.3852557734 411849.6517192838, " +
                "641853.7924351022 411866.8991175313, " +
                "641868.09 411913.34)), " +
                "((641917.6679652191 411902.33038010733, " +
                "641901.3863761591 411849.65131326165, " +
                "641901.3857792952 411849.65152956214, " +
                "641917.6675451562 411902.3304447612, " +
                "641917.6679652191 411902.33038010733)))";

public static void main(String[] args) throws Exception {
    Geometry input = new WKTReader().read(WKT);

    Geometry snapped =
            GeometrySnapper.snapToSelf(input, 0.005, false);

    Geometry snappedAndCleaned =
            GeometrySnapper.snapToSelf(input, 0.005, true);

    System.out.println("Input valid: " + input.isValid());
    System.out.println("Input area: " + input.getArea());

    System.out.println();
    System.out.println("snapToSelf(cleanResult=false)");
    System.out.println("Valid: " + snapped.isValid());
    System.out.println("Area: " + snapped.getArea());
    System.out.println(snapped);

    System.out.println();
    System.out.println("snapToSelf(cleanResult=true)");
    System.out.println("Valid: " + snappedAndCleaned.isValid());
    System.out.println("Area: " + snappedAndCleaned.getArea());
    System.out.println(snappedAndCleaned);
}

}`

Start with GeometrySnapper.snapToSelf and run the SnapToSelfReproducer using the supplied WKT, tolerance, and cleanResult values. Compare validity, area, and polygonal output for both modes; done means self-snapping no longer creates invalid topology or an unexpected cleaned result.