Ensure that reference lines appear in single value bar/line plots

[rich-iannone]

Right now the reference_line= argument does not display a reference line when making a nanoplot from a single value. From question in the gt_package Discord channel, @MarcoGorelli asked to make this example work (and I filled in the GT part here):

import polars as pl
from great_tables import GT

data = pl.DataFrame({
    'Library': ['pandas (including NumPy)', 'pandas (including NumPy and PyArrow)', 'Polars'],
    'Size (MB)': [163, 290, 85],
}).sort('Size (MB)')

GT(data).fmt_nanoplot(columns="Size (MB)", plot_type="bar", reference_line=275)

Currently this results in:

The desired result should instead be something like this:

[marcozzxx810]

@rich-iannone, I have tried out to use reference_line="min", resulting the same graph.

does it supposed to work when using keywords?

import polars as pl
from great_tables import GT

data = pl.DataFrame({
    'Library': ['pandas (including NumPy)', 'pandas (including NumPy and PyArrow)', 'Polars'],
    'Size (MB)': [163, 290, 85],
}).sort('Size (MB)')

GT(data).fmt_nanoplot(columns="Size (MB)", plot_type="bar", reference_line="min")