Fix IMU linear acceleration frame differentiation

[sylvesterkaczmarek]

Description

Fix IMU linear acceleration for rigid bodies that rotate while translating.

Both the current experimental implementation and the deprecated IMU implementation rotated world-frame linear velocity into the sensor frame before finite differencing it. Because the sensor frame changes while the body rotates, differencing those rotating-frame components produces incorrect apparent acceleration.

The fix keeps linear velocity in the inertial world frame through the finite-difference/filter step, then rotates the resulting acceleration into the current sensor frame. Angular velocity and orientation handling are unchanged.

This PR addresses only the confirmed differentiation-frame bug from #735; the separate COM/lever-arm enhancement mentioned there is out of scope.

Validation

• adds a regression test with constant world-frame linear velocity and simultaneous angular velocity
• true inertial linear acceleration in that case is zero
• current and deprecated implementations are updated consistently
• new Python regression test passes py_compile
• patch passes git diff --check

Fixes #735.