Assembly3: Solver speed debug

[project4]

An update:
I opened the document of the round parts and set "Skip recompute" in it's document.
Doing that dropped the movement time to 6 seconds (about half!).
That's pretty strange since its a single body part, no assembly around it in the child document.

Also, looks like there's another bug hiding: changing the "Skip recompute" flag doesn't set the document as changed...