feat(cleaner): ✨ add command prune

this new command will be called by cron-like process to clean purge old logs and old mails. All files were formatted and mail_utils was renamed in utils since it now defines utility function not only for mail functions.

tests/test_logging.py

@@ -20,7 +20,7 @@ def test_setup_handler(tmp_log_file):
 
 def test_count_of_handler(tmp_log_file):
     """Assert `setup_handler` instanciate exactly one StreamHandler and one FileHandler.
-    
+
     Must have exactly two handlers in total.
     """
     logger = getLogger()
@@ -82,7 +82,7 @@ def test_modified_format():
 
 def test_logging_in_correct_path(tmp_log_file):
     """Assert log file is correctly written in output directory.
-    
+
     Check content of the file. It must contain logs from CRITICAL to DEBUG level.
     """
     logger = logging.getLogger("logwatcher")