fix: synchronise element bindings

[Rich-Harris]

#10511

just a failing test for now

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[dummdidumm]

Gave this a go and quickly fell down a rabbit hole of how to solve the bind_this bugs and timing stuff around this. TLDR the current way does not work for arrays, what we need is to have a way to access the previous index to nullify it in case an item moves. Looking into that right now.

[dummdidumm]

Turned out to be very easy fix once #10598 was implemented. I think we used the animation frame dance previously where the $effect timing was slightly different and not wait on its children before rerunning. With that now everything false into place nicely.