[Feat/bug] Make `hidden` work for clientside callbacks

[antonymilne]

I love the new hidden=True feature introduced in #3407 to hide callbacks from the devtools graph, but unfortunately it doesn't do anything for clientside callbacks. In practice this unfortunately makes it completely useless for our purposes since all the callbacks we want to hide happen to currently be clientside 😅

Is there any way hidden could be implemented for clientside callbacks too, pretty please? 🙏

From reading the PR and docs it wasn't clear to me whether this was a bug or just an un-implemented feature, so not quite sure how to classify the PR. Either way I would be hugely grateful if this could be added. Happy to raise the PR myself if it sounds like a good idea.

[robertclaus]

Good idea! We likely won't get to this in the next few months, but would be thrilled to review a PR for it!