fix asymmetry due to trigonometric inaccuracies and fix rotor average problem in fuga

py_wake/deficit_models/fuga.py

py_wake/deficit_models/selfsimilarity.py

py_wake/rotor_avg_models/rotor_avg_model.py

py_wake/tests/test_deficit_models/test_deficit_models.py

py_wake/tests/test_deficit_models/test_rotor_avg_models.py

.../test_wind_farm_models/test_enginering_wind_farm_model.py

py_wake/wind_farm_models/engineering_models.py