Me again ;-)

Similar to the Github activity heatmap I'd like to suggest to make it possible to show tooltips with some user-definable contents (based on the data attributes for each day, maybe). I've found tippy and a Svelte integration. I've done some basic testing to see how this works with SVG, it does.

However, I am at a loss as to how to combine your component and this one. As a Svelte newbie, I'd appreciate a pointer so that I could maybe provide a PR, or if this doesn't make sense, an idea on how to combine the two components.