This took me a while to figure out. We no longer visit all 9 block
around and with the touched node, but instead visit adjacent plus
self. We then walk -non- recursively through all neigbors and if
they cause a nodeupdate, we just keep walking until it ends. On
the way back we prune the tail.
I've tested this with 8000+ sand nodes. Video result is here:
https://youtu.be/liKKgLefhFQ
Took ~ 10 seconds to process and return to normal.
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