Add initial test framework for utils functions

Added the initial test framework that will eventually encompass all of the functions in the package. Started with the primary utility functions since those are widely used and also simple enough to get used to writing tests. All current tests pass 😁

src/rc_gpfs/utils/core.py

@@ -8,7 +8,7 @@ import pyarrow.parquet as pq
 import numpy as np
 
 from .units import as_bytes, convert_si, create_size_bin_labels
-from .datetime import *
+from .datetime import as_datetime,create_timedelta_breakpoints,create_timedelta_labels
 
 def parse_scontrol():
     job_id = os.getenv('SLURM_JOB_ID')