Grid traversal mispredicts & gird position/rotation prediction

[ElectroJr]

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Currently moving on and off rotating grids mispredicts badly. this partly due to stuff fixed in #2932, and (apparently) partly because the client disables physics prediction for everything other than players & dragged objects, including grids.

Enabling physics prediction, together with #2932, results pretty smooth grid traversal, up until grids are spinning at silly speeds.

There might be some way of fixing this without enabling prediction for grids. I'm not even sure WHY it makes it mispredict quite as badly as it does, just that it appears to fix it.