Construct a matrix from unity's inertiaTensor and inertiaTensorRotation fields

UnityInertiaTensor.cs

// Returns the INVERSE inertia tensor in GLOBAL space (not local!)
// Returns a Matrix3x3, but there's no type for that, so waste some space with a Matrix4x4
// Equivalent to GetInertiaTensorGlobal(rb).inverse, but faster
private static Matrix4x4 GetInverseInertiaTensorGlobal(Rigidbody rb) {
    Vector3 inertiaTensor = rb.inertiaTensor;
    Vector3 inverseInertiaTensor = new(1 / inertiaTensor.x, 1 / inertiaTensor.y, 1 / inertiaTensor.z);
    Matrix4x4 rotation = Matrix4x4.Rotate(rb.rotation * rb.inertiaTensorRotation);
    // rotation is orthonormal, so inverse=transpose
    return rotation * Matrix4x4.Scale(inverseInertiaTensor) * rotation.transpose;
}
// -- some other similar helpers --
private static Matrix4x4 GetInverseInertiaTensorLocal(Rigidbody rb) {
    Vector3 inertiaTensor = rb.inertiaTensor;
    Vector3 inverseInertiaTensor = new(1 / inertiaTensor.x, 1 / inertiaTensor.y, 1 / inertiaTensor.z);
    Matrix4x4 rotation = Matrix4x4.Rotate(rb.inertiaTensorRotation);
    return rotation * Matrix4x4.Scale(inverseInertiaTensor) * rotation.transpose;
}
private static Matrix4x4 GetInertiaTensorGlobal(Rigidbody rb) {
    Matrix4x4 rotation = Matrix4x4.Rotate(rb.rotation * rb.inertiaTensorRotation);
    return rotation * Matrix4x4.Scale(rb.inertiaTensor) * rotation.transpose;
}
private static Matrix4x4 GetInertiaTensorLocal(Rigidbody rb) {
    Matrix4x4 rotation = Matrix4x4.Rotate(rb.inertiaTensorRotation);
    return rotation * Matrix4x4.Scale(rb.inertiaTensor) * rotation.transpose;
}