l1agen_oci - Speed up _SPEC file processing

Whenever there is a _SPEC file, even if it only has 100 scans it takes much longer than your average science data file with over 1000 scans. Investigate to see what is causing the slow down and see if you can speed it up.

When running PACE_OCI_SPEC.20250904T215442.L1A.nc., you will have a _SPEC file in between 2 science files. The _SPEC one takes at least 10-15 mins to complete ~100 scans while both science files takes around 3 mins with > 1000 scans. Maybe _SPEC does more so will need to dig deeper into what it's doing.