fix: object overwriting when using multiple charts

[BitTheByte]

This PR fixes an overwrite bug in the DEFAULT_CHART_OPTIONS as it was shared and mutated between chart instances resulting in a wrong rendering.

Before:

After:

[lukasvinclav]

@BitTheByte thank your very much for PR. Would you mind to provide use-case how I can replicate the issue in the screenshot above? I want to test the functionality but I'm not sure where to start.