run linter and update reused variable name

run linter and update reused variable name

backend/src/xfd_django/xfd_api/helpers/date_time_helpers.py

@@ -1,12 +1,15 @@
 """Helper methods to deal with date and time manipulation."""
+# Standard Python Libraries
 import datetime
 
-def calculate_days_back(days_ago:int):
+
+def calculate_days_back(days_ago_int: int):
+    """Create a date string of a calculated past date."""
     # Step 1: Get the current date and time in UTC
     current_time = datetime.datetime.now(datetime.timezone.utc)
     # Step 2: Subtract days from the current date
-    days_ago = current_time - datetime.timedelta(days=days_ago)
+    days_ago = current_time - datetime.timedelta(days=days_ago_int)
     # Step 3: Convert to an ISO 8601 string with timezone (e.g., UTC)
     since_timestamp_str = days_ago.isoformat()
 
-    return since_timestamp_str
+    return since_timestamp_str