/// An enumeration representing how bars are displayed when multiple bar traces share the same axis.
///
/// # Example
///
/// ```rust
/// use plotlars::{BarMode, BarPlot, Plot};
/// use polars::prelude::*;
///
/// let dataset = df![
/// "animal" => &["giraffe", "giraffe", "orangutan", "orangutan", "monkey", "monkey"],
/// "gender" => &["female", "male", "female", "male", "female", "male"],
/// "value" => &[20.0f32, 25.0, 14.0, 18.0, 23.0, 31.0],
/// ]
/// .unwrap();
///
/// BarPlot::builder()
/// .data(&dataset)
/// .labels("animal")
/// .values("value")
/// .group("gender")
/// .mode(BarMode::Stack)
/// .build()
/// .plot();
/// ```
///
/// 