Remove timedelta values less than or equal to 0

When creating timedelta breakpoints and labels for grouping, any timedelta values less than or equal to 0 don't make sense and should be removed automatically

src/rc_gpfs/utils/datetime.py

@@ -20,7 +20,7 @@ def create_timedelta_breakpoints(
     delta_unit: Literal['D','W']
 ) -> List[np.datetime64]:
     run_date = as_datetime(run_date)
-    return [run_date - as_timedelta(c,delta_unit) for c in delta_vals]
+    return [run_date - as_timedelta(c,delta_unit) for c in delta_vals if c > 0]
 
 def create_timedelta_labels(
     delta_vals: int | List[int],