Duplicate legend entries when plotting on sliced spanned axes with `legend=True`

[ToryDeng]

When creating a figure with a spanned subplot layout using a 2D array, slicing the axes grid to access the spanned subplot (e.g., axs[0, :2]) and calling .scatter() with legend=True results in duplicate legend entries.

Reproducible Example:

import numpy as np
import ultraplot as uplt

array = np.array(
    [[0.71510417, 0.18342202],
    [0.63857324, 0.49007551],
    [0.34293048, 0.81424364],
    [0.93123847, 0.54010325],
    [0.12053916, 0.67823549]]
)

fig, axs = uplt.subplots(np.array([[1, 1, 2], [3, 4, 5]]))
ax = axs[0, :2] 

ax.scatter(
    x=array[:, 0], y=array[:, 1], c="grey", label="data", legend=True
)

A quick workaround is to replace ax = axs[0, :2] with ax = axs[0]. However, I'm not sure if this duplicate behavior is intended, or if the usage of axs[0, :2] is simply discouraged in ultraplot.

[cvanelteren]

I think the issue is that the indexing is using two subplots in this example. It is definitely a bug and should be addressed.

[cvanelteren]

Will have a look!

[cvanelteren]

Fixed on #598 will merge soon.