fix(io): add missing data for saving fiducial ruler and included unit test
Description
When we create a ruler fiducial in update_image_distance_field() in ruler.cpp, we now set a sop_instance_uid for fiducials if it has no value. By doing this, we are able to save ruler fiducials in a DICOM file.
Also provide an unit test on the reader/writer for ruler fiducials.
Changes made
Instead of set a sop_instance_uid for fiducials in update_image_distance_field() in ruler.cpp, we set this in the writer file.cpp. Because it is required to create a correct header for a DICOM file, it would be more logical to have this code in the writer.
How to test it?
Run tests, specifically check io_dicom_ut, where ruler_fiducials_reader_writer_test is. Verify if in the /tmp/RulerFiducialsReaderWriterTest if the fiducials DICOM isn't empty.
For a complete test, this fix is used in a dependent merge-request.