Support linspace and interval wrapper for datetime and float about plotters

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This is because we currently don't have the time-slice type. Because it's not well-defined for a histogram on DateTime type, since we don't know the bucket size. (For example, one bar per 5 minutes, etc...)

The type slice coordinate should be added. But before that happens, you actually can draw a histogram without using the Histogram help. Since all the series types are just defined for convenience.

As you know the series is just a iterator of element, Thus for your case, you can actually have things like that:

    let histogram_values: Vec<(DateTime, f32)>;
    chart.draw_series(histogram_values.iter().map(|(time, value)| {
        Rectangle::new(
            [(time, value), (time + Duration::minutes(5), value)],
            RED.filled(),
        )
    }))?;

This should just work. But you are right, the time slice should be supported.

In addition, Date is automatically sliced, because it has minimal resulution which is 1 day.

For the same reason, the float number can't use the Histogram type, but integer can.