refactor: modernize annotation auxiliary data and strengthen ECG tests

• Replace raw char** AUX auxiliary annotation storage with std::vector<std::string>
• Remove manual AUX memory management from constructor, destructor, and reset
• Update GetAuxData() to return the vector-based auxiliary data
• Improve ECG feature extraction test setup and input-size validation
• Add null-safe annotation type handling in dataset tests
• Enable physiological range assertions for extracted heart rate and waveform features
• Remove obsolete debug code and disable outdated BIDMC and SIM-3 validation tests
• Clean up annotation reset and dataset setup code
• Change lastR to last_R in ClinicalECGEngine.h & ClinicalECGEngine.cpp
• Configure codespell to ignore the ect word