ratatui: Barchart doesn't render labels in entire width

Description

The barchart widget doesn’t render labels that are the full width (this affects both non-unicode and unicode)

To Reproduce

fn render_simple_barchart(area: Rect, buf: &mut Buffer) {
    let data = [
        ("Sat", 76),
        ("Sun", 69),
        ("Mon", 65),
        ("Tue", 67),
        ("Wed", 65),
        ("Thu", 69),
        ("Fri", 73),
    ];
    let data = data
        .into_iter()
        .map(|(label, value)| {
            Bar::default()
                .value(value)
                // cannot use this until the column width bug is fixed
                .text_value(format!("{}°", value))
                .label(label.into())
        })
        .collect_vec();
    let group = BarGroup::default().bars(&data);
    BarChart::default()
        .data(group)
        .bar_width(3)
        .bar_gap(1)
        .render(area, buf);
}

with the following line removed:

                .text_value(format!("{}°", value))

And the same occurs replacing that with

                .text_value(format!("{}x", value))

Expected behavior

I think this should probably render like the following (hacking a couple of things in the barchart implementation to make it work):

Environment

Mac/iterm/FiraCode(NF)/main/crossterm

Additional context

• Is this expected behavior for some historical reason?
• If this is expected, how should it be documented?
• What significance should unicode play here (e.g. the degree symbol has string len = 2 and unicode width = 1)? Is #75 relevant to the degree symbol?
• What is the history of this? Check for any guidance from commits, and comments on PRs/ issues in Ratatui and tui-rs.