Add Support for Global Figure Titles

[isofer]

Arvis Plots currently supports setting titles on individual subplots, but there is no option to define a title for the entire figure. This makes it difficult to label multi-panel figures or provide an overall description of the visualization. It would be helpful to have a way to set a global figure title directly, similar to what other plotting libraries offer. This would improve readability and presentation quality for users who need a single, centralized title.