a/tracking: Migrate C++ APIs to the official namespaces now that we have some.

src/xrt/auxiliary/tracking/t_calibration.cpp

src/xrt/auxiliary/tracking/t_calibration_opencv.hpp

src/xrt/auxiliary/tracking/t_file.cpp

src/xrt/auxiliary/tracking/t_fusion.hpp

src/xrt/auxiliary/tracking/t_helper_debug_sink.hpp

src/xrt/auxiliary/tracking/t_imu.cpp

src/xrt/auxiliary/tracking/t_imu_fusion.hpp

src/xrt/auxiliary/tracking/t_lowpass.hpp

src/xrt/auxiliary/tracking/t_lowpass_vector.hpp

src/xrt/auxiliary/tracking/t_tracker_hand.cpp

src/xrt/auxiliary/tracking/t_tracker_psmv.cpp

src/xrt/auxiliary/tracking/t_tracker_psmv_fusion.cpp

src/xrt/auxiliary/tracking/t_tracker_psmv_fusion.hpp

src/xrt/auxiliary/tracking/t_tracker_psvr.cpp

src/xrt/auxiliary/tracking/t_tracking.h