thomasb-gr

### Description [`polars.DataFrame.head(n)`](https://docs.pola.rs/py-polars/html/reference/dataframe/api/polars.DataFrame.head.html#polars.DataFrame.head) supports negative `n` to fetch all but the last `n` rows, but [`DataFrame.group_by.GroupBy.head(n)`](https://docs.pola.rs/py-polars/html/reference/dataframe/api/polars.dataframe.group_by.GroupBy.head.html#polars.dataframe.group_by.GroupBy.head) does not offer the same functionality. I can work around this by calculating the...