No pushdown filters applied if temporal type was optimized into timestamp type by datafusion

[omerhadari]

When running queries such as SELECT * FROM table WHERE ts_col = CAST('2024-01-01 00:12:34' AS TIMESTAMP), Datafusion converts the Cast directly to a TimestampNanosecond type. This is not handled by the code in here.

Test for example that shows the issue:

    #[test]
    fn test_comparison_with_nanos_work() {
        let left = Expr::Column(Column::new_unqualified("ts"));
        let right = Expr::Literal(ScalarValue::TimestampNanosecond(Some(1000), None));
        let op = Operator::GtEq;
        let binary_expr = Expr::BinaryExpr(BinaryExpr::new(Box::new(left), op, Box::new(right)));
        let predicate = convert_filters_to_predicate(&vec![binary_expr]).unwrap();
        let expected_predicate =
            Reference::new("ts").greater_than_or_equal_to(Datum::timestamp_nanos(1000));
        assert_eq!(predicate, expected_predicate);
    }

Note:
The correct type of Datum should be handled in values.rs, otherwise the issue will manifest as a failure to cast timestamp to whatever it's compared to.