Relation.structure() fails for TableSlice with ClassCastException

[brainbytes42]

Hi,

for a slice from a TableSliceGroup, a call to structure fails with an Exception:
java.lang.ClassCastException: class tech.tablesaw.api.DoubleColumn cannot be cast to class tech.tablesaw.api.IntColumn (tech.tablesaw.api.DoubleColumn and tech.tablesaw.api.IntColumn are in unnamed module of loader 'app')

This was the case for a table with different columns of "real data", but is the same for this following small example:

import tech.tablesaw.api.StringColumn;
import tech.tablesaw.api.Table;
import tech.tablesaw.table.TableSlice;
import tech.tablesaw.table.TableSliceGroup;

public class SliceTest {

    public static void main(String[] args) {

        Table table = Table.create(StringColumn.create("MyCol", "A", "A", "B"));

        TableSliceGroup sliceGroup = table.splitOn("MyCol");

        System.out.println("++++++++++ structure() for slice fails ++++++++++");

        for (TableSlice slice : sliceGroup.getSlices()) {
            System.out.println("slice: " + slice);
            System.out.println();
            try {
                System.out.print("slice.structure(): ");
                System.out.println(slice.structure()); // FAILS
            } catch (ClassCastException e) {
                System.out.println(e);
            }
            System.out.println();
        }

        System.out.println();
        System.out.println("++++++++++ ... but structure() for slices as tables works ++++++++++");

        for (Table tableListTable : sliceGroup.asTableList()) {
            System.out.println("tableListTable: " + tableListTable);
            System.out.println();

            System.out.println("tableListTable.structure(): ");
            System.out.println(tableListTable.structure());

            System.out.println();
        }

    }

}

I've tested it with Amazon Corretto 16 and tablesaw-core:0.38.2 / 0.38.3

[lwhite1]

fixed