`max` with more than one selected column on `Pivot` aggregates each column separately in Notebooks

```kotlin
df.pivot { isHappy }.max { age and weight }
```
in a Gradle project results in:
finding the maximum value among all the selected columns.

But in Kotlin Notebooks it results in:
finding the maximum for each column separately.

The expected behavior is as in the Gradle project.

Reproduce the `df.pivot { isHappy }.max { age and weight }` example in both a Kotlin Notebook and a Gradle project, comparing the aggregation results. Investigate the notebook-specific behavior; done means the Kotlin Notebook matches the Gradle result by finding one maximum across the selected columns.

Written by the indexing model from the issue text.