test_hingedRigidBodyDefaultConfig

Regression test for issue #469: the constructor used to call this->IPntS_S.Identity() and this->dcm_HB.Identity() as statements. Eigen::Matrix3d::Identity() is a static factory whose return value was discarded, so the members were left uninitialized instead of defaulting to identity. This test asserts a freshly constructed effector exposes identity defaults for both members.

test_hingedRigidBodyDefaultConfig.test_defaultDcmAndInertiaAreIdentity()

A fresh effector must default dcm_HB and IPntS_S to identity.