Add centripetal acceleration to the simulated IMU

[clmazzac]

Problem

The simulated IMU reports no lateral acceleration in a turn.

captureVehicleSnapshot takes body acceleration from the derivative of body-frame velocity. The body frame rotates with the vehicle, so that derivative omits omega x v. In a steady turn the body-frame velocity stays (speed, 0, 0), and the result is zero. A real accelerometer reads speed * yaw rate toward the turn.

A filter that uses lateral acceleration then sees a reading that contradicts the gyro. An EKF with the measurement model a_y = v * omega drove its speed estimate toward zero in each turn.

Fix

Add the omega x v term to the body acceleration in captureVehicleSnapshot:

• a_y += yawRate * v_x
• a_x -= yawRate * v_y

Only the IMU reads bodyAcceleration.

Measurements

One scenario, run before and after: about 90 m with two turns, route follower at 3 m/s. IMU messages were recorded from the orchestrator. The internal pose came from the run's SFLog. Both runs also had #5 applied. This change does not depend on #5.

Check	Before	After
IMU linear_acceleration.y vs speed x yaw rate, while turning (least-squares slope)	0.000	+1.008
Largest linear_acceleration.y in a turn	0.07 m/s²	2.40 m/s² (expected up to 2.27)
IMU gyro z, accel x, accel z, 3,620 samples		bit-for-bit the same
GNSS latitude and longitude, 362 fixes		the same

Effect on an external EKF (IMU yaw rate, lateral acceleration and GNSS), position error against visualization.localization.error:

	Before	After
Mean	2.45 m	0.18 m
Max	7.36 m	1.62 m
In the two turns (mean)	4.91 m, 1.99 m	0.19 m, 0.22 m

Tests

• npm test: 1,892 of 1,899 pass. The one failure, Python decodes retained RGB, depth, and CameraInfo SFLog messages, also fails on main on my machine.
• Two new tests in localization-sensors.test.js:
  • a steady turn reads speed * yaw rate on IMU y, with the sign of the turn, for both directions. This test fails on main.
  • straight driving reads no lateral acceleration.

Not in this change

An IMU mounted away from the vehicle reference point also feels terms from that offset (alpha x r and omega x (omega x r)). The default IMU sits at the reference point, so this change omits them.

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