MNT/FIX: Rename Lo background column to rate/sigma instead of type (#2639)

Author: greglucas

imap_processing/lo/l1c/lo_l1c.py

@@ -1078,9 +1078,9 @@ def set_background_rates(
         # for each energy step, set the background rate and uncertainty
         for esa_step in range(0, 7):
             value = row[f"E-Step{esa_step + 1}"]
-            if row["type"] == "rate":
+            if row["rate/sigma"] == "rate":
                 bg_rates[esa_step, bin_start:bin_end, :] = value
-            elif row["type"] == "sigma":
+            elif row["rate/sigma"] == "sigma":
                 bg_sys_err[esa_step, bin_start:bin_end, :] = value
             else:
                 raise ValueError("Unknown background type in ancillary file.")

imap_processing/tests/lo/test_anc/imap_lo_hydrogen-background-small_20250101_20270101_v001.csv

@@ -1,4 +1,4 @@
-YYYYDDD,GoodTime_start,GoodTime_end,bin_start,bin_end,Lo,E-Step1,E-Step2,E-Step3,E-Step4,E-Step5,E-Step6,E-Step7,type
+YYYYDDD,GoodTime_start,GoodTime_end,bin_start,bin_end,Lo,E-Step1,E-Step2,E-Step3,E-Step4,E-Step5,E-Step6,E-Step7,rate/sigma
 2025001,473389200.0,473472000.0,0,1,Lo,0.0098,0.0089,0.0118,0.0113,0.0056,0.0008,0.0000,rate
 2025001,473389200.0,473472000.0,0,1,Lo,0.0025,0.0020,0.0015,0.0015,0.0010,0.0008,0.0000,sigma
 2025001,473389200.0,473472000.0,1,2,Lo,0.0098,0.0089,0.0118,0.0113,0.0056,0.0008,0.0000,rate

imap_processing/tests/lo/test_anc/imap_lo_oxygen-background-small_20250101_20270101_v001.csv

@@ -1,4 +1,4 @@
-YYYYDDD,GoodTime_start,GoodTime_end,bin_start,bin_end,Lo,E-Step1,E-Step2,E-Step3,E-Step4,E-Step5,E-Step6,E-Step7,type
+YYYYDDD,GoodTime_start,GoodTime_end,bin_start,bin_end,Lo,E-Step1,E-Step2,E-Step3,E-Step4,E-Step5,E-Step6,E-Step7,rate/sigma
 2025001,473389200.0,473472000.0,0,1,Lo,0.0098,0.0089,0.0118,0.0113,0.0056,0.0008,0.0000,rate
 2025001,473389200.0,473472000.0,0,1,Lo,0.0025,0.0020,0.0015,0.0015,0.0010,0.0008,0.0000,sigma
 2025001,473389200.0,473472000.0,1,2,Lo,0.0098,0.0089,0.0118,0.0113,0.0056,0.0008,0.0000,rate