Retrieve samples outrates

Using a working_directory (HPC or local), the sampling outrates csv are not well produced.

They are stored in the working directory and never copied to output_folder.

This is a silent error, as the function used to concatenate the files at the end of the workflow do nothing if the list of input file is empty.

This MR correct this behaviour, update the test using the working dir to ensure the file is well created at the end + some pylint and docstring correction.

All TU pass. TI pass too.