Support GROUP BY ALL

DuckDB supports this: https://duckdb.org/2022/05/04/friendlier-sql.html:

```
SELECT
systems,
planets,
cities,
cantinas,
SUM(scum + villainy) as total_scum_and_villainy
FROM star_wars_locations
GROUP BY ALL
-- GROUP BY systems, planets, cities, cantinas
```

It's essentially a shortcut to refer to all dimension fields in a group by.

Start with the DuckDB GROUP BY ALL reference linked in the issue and inspect the parser's existing GROUP BY handling; no file or test path is named. Done means the example syntax is accepted and coverage verifies that GROUP BY ALL represents grouping by all dimension fields.

Written by the indexing model from the issue text.