fix: acceleration still applied while PhysicsTime is paused

[jcornaz]

fix #251.

Thanks @cark for the bug report.

[github-actions]

🎉 This issue has been resolved in version 3.1.0 🎉

[cark]

Thanks !
I'll be testing this during next week.
While this is probably good for my use case, looking at the code I can't help but wonder about slow or fast motion.
I thought you would work this fix through the PhysicsTime. Though this is probably me misunderstanding the whole thing !

Anyways, good enough for me, thanks again.

[jcornaz]

For slow/fast motion, rapier is supposed to handle it. As Heron is only the API, and rapier is responsible for the simulation itself.