MEKF redesign

[vegard-solum-4ss]

Description

Refactor MEKF for readability and speed (AHRS/VRU mode).

Runs >70% faster than current implementation.

Key improvements:

• Calculate state transition matrix and process noise covariance directly, avoiding the intermediate continuous-time state space matrices.
• Remove the need for prior state and covariance estimates.
• Simplified Kalman update code.
• Take coning and sculling integrals as input instead of instantaneous rate measurements. Note that rate measurements can still be applied using dvel = f * dt and dtheta = w * dt.
• Speed-up attitude reset by exploiting the renormalization.

Checklist

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