Add file type for OMPS total SO2 (V8TOS) in omps_edr reader

[djhoese]

This PR adds support for the SO2 EDR files for the OMPS reader (omps_edr). The basic functionality was easy to add, but getting filtering to do something useful and remove noise took some time. There were differences between what the file says to do: _FillValue/valid_ragne versus other non-CF values versus what the algorithm developer said should be done versus what was actually done on the JSTAR Mapper website to get the data prepared for visualization. More detailed discussion can be found in the Polar2Grid issue related to this (ssec/polar2grid#820). What we landed on was something in between what the algorithm developer said to do and what JSTAR Mapper was doing with IDL code. The basic idea is that there is an ErrorFlag variable that can be used for basic quality filtering but for SO2 variables it seems to do very little. The other filtering option is to remove any negative values from the SO2 column amount fields. JSTAR Mapper chooses to remove anything below 1, but we didn't quite agree with remove real values between 0 and 1. Both these types of filtering are off by default in Satpy (we'll the negative filter on by default in P2G).

This PR also rewrites some of the tests for this reader as Claude discovered some inconsistencies with real files and between the Ozone files and the SO2 files.

CC @kathys

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

❌ Patch coverage is 98.42520% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.35%. Comparing base (17bf08d) to head (07d9bcf).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
satpy/readers/omps_edr.py	92.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3455    +/-   ##
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  Coverage   96.34%   96.35%            
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  Files         465      465            
  Lines       59151    59327   +176     
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+ Hits        56990    57163   +173     
- Misses       2161     2164     +3     

Flag	Coverage Δ
behaviourtests	3.57% <0.00%> (-0.02%)	⬇️
unittests	96.44% <98.42%> (+<0.01%)	⬆️

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