Support curved line parallel coordinate plot

[Alnusjaponica]

Motivation

If lines of similar colors intersect in a parallel coordinate plot, it is challenging to discern how the lines connect when only straight lines are used. Adding an option to curve the plots makes it easier to distinguish each trial. Examples of parallel coordinate plots with curved lines can be found at https://docs.wandb.ai/guides/app/features/panels/parallel-coordinates. or https://static.googleusercontent.com/media/research.google.com/ja//pubs/archive/46180.pdf.

Description

Some libraries with this feature, such as Vizier or W&B, do not reveal the implementation and currently plotly does not have such option (See plotly/plotly.py#2991) but there is an interesting answer on Stack Overflow. It might be a good start to examine how this strategy works.

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