Better cache vehicle mass center

[SurFlurer]

Is your feature request related to a problem? Please describe.

map::vehmove() has to call vehicle::calc_mass_center() multiple times in a turn. This results in around 20% of total overhead for driving large deathmobiles. It seems that the code already handles some cache of the mass center. However, it is clearly not particularly good at reducing overhead.

Solution you would like.

Have a better cache of the mass center. This change can hopefully save 75% of this function's overhead per turn.

Maybe we should add a set of different functions to "cheaply" handle mass changes caused by fuel drain?

Describe alternatives you have considered.

No response

Additional context

This is somewhat meaningful to finish this to smooth the transition towards the removal of charge from solid comestibles.

[SurFlurer]

Now what's left to do is to add a fast way to recalc mass center for every-turn consumption of fuel.

[github-actions[bot]]

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