Improve Anim

[twitwi]

• Rework @code @codec @math @step etc so that they are uniform, ideally without variants (just @code, @math) and use generic things like {3-4} for highlight vs 3-4 for show
• Refactor the above rework and add @child
• Allow the same across shadowRoot [...temp0.querySelectorAll(".mermaid")].flatMap(e=>[...e.shadowRoot.querySelectorAll('::part(sr)')]) (<- a kind of polyfill, as it works in css not js, or with deprecated custom ::shadow) ... ie, split the string at ::part and do the cascade)
• Consider more coherent stuff as {} highlight only the specified but [] shows the specified (does not hide the rest), either have another ()? or document the use of {} with some CSS to make it appear/hide
• Test the use of clickElements (as in the CodeWrapper) to have a no-bug integration with pdf export -> was done, but remove the -1 (it is there in the CodeWrapper but I'm not sure why and it cause the missing last step in the overview)
• Allow to play/pause/seek videos, need to be synced across views...
• Make/update the demo accordingly