Rename test functions from test_image_addition to test_image_sum and test_signal_addition to test_signal_sum for consistency

Author: PierreRaybaut

cdl/tests/features/images/operation_unit_test.py

@@ -448,7 +448,7 @@ def test_image_rotate() -> None:
 
 
 if __name__ == "__main__":
-    test_image_addition()
+    test_image_sum()
     test_image_average()
     test_image_product()
     test_image_division()

cdl/tests/features/signals/operation_unit_test.py

@@ -252,7 +252,7 @@ def test_signal_arithmetic() -> None:
 
 
 if __name__ == "__main__":
-    test_signal_addition()
+    test_signal_sum()
     test_signal_average()
     test_signal_product()
     test_signal_difference()