Performance: throttled status update loop impacts performance on large notebooks

[fonsp]

In large notebooks, the throttled update loop from the status tree, i.e.:

Pluto.jl/src/webserver/SessionActions.jl

Lines 189 to 192 in 8b7a65d

	notebook.status_tree.update_listener_ref[] = first(throttled(1.0 / 20) do
	# TODO: this throttle should be trailing
	Pluto.send_notebook_changes!(Pluto.ClientRequest(; session, notebook))
	end)

Can slow down the notebook. When the notebook is large, and you are moving sliders, this can halve the update speed.

Ideas:

• During reactive run, share the throttled update with the new one.
• Throttle rate should adapt to the time it takes to update clients.
• It also looks like there is a bug in the throttle code: the throttled code runs in batches of 2...