Apply scalebar length to subcoordinate_y range

[droumis]

Fixes #6416

Enabling subcoordinate_y should now apply the scalebar length relative to the subcoordinate_y range.

Code

import holoviews as hv
import numpy as np
import panel as pn
pn.extension()
hv.extension("bokeh")


common_opts = dict(subcoordinate_y=True, scalebar_unit=("cm", "m"), color="lightgrey")

curves = []
for i in range(10):
    curves.append(hv.Curve(np.random.rand(1000), label=f'c{i}').opts(**common_opts, scalebar=True if i == 5 else False))

curves = hv.Overlay(curves).opts(show_legend=False)

pn.panel(curves.opts(width=800, height=600)).servable()