egui_extras: verical separator beween columns

I make an example of a table with ASCII characters:
```
+-----------++-----------+
| a | b | c || d | e | f |
|-----------++-----------|
| 1 | 2 | 3 || 4 | 5 | 6 |
|-----------++-----------|
| 1 | 2 | 3 || 4 | 5 | 6 |
+-----------++-----------+
```

In this case, I'd like to put a separator between the 3rd and 4th column. A black vertical line, or something...
Is there a way to do it?

The issue describes an egui_extras table with a separator between the third and fourth columns, but names no source file, example, or test. Start by locating the table API and reproducing the layout shown in the issue. Done means there is a documented or implemented way to render a visible vertical separator between those column groups, with coverage if the project has relevant table tests.

Written by the indexing model from the issue text.