Plot lines with round cap style

This is the issue:

Maybe useful resources:
https://matplotlib.org/stable/gallery/lines_bars_and_markers/capstyle.html
https://stackoverflow.com/questions/11578760/matplotlib-control-capstyle-of-line-collection-large-number-of-lines

No project file, test, or entry point is named. Start by reviewing the issue image and the linked Matplotlib capstyle example, then locate the code that draws these lines; done means the rendered line ends visibly use a round cap style without breaking existing plots.

Written by the indexing model from the issue text.