MUL-283: Simplify MARS2GRIB mapping

[pgeier]

Description

Removed special handling for levtype al and spherical harmonics in the entry rule mars2grib/Rules.cc.

Before AL and SH had there own path. SH fields had there own specific levtype + param -> typeOfLevel mapping.
As a result params had to be added frequently instead of making the mapping othogonal.
The split in the mapping dates back to when the rules where generated through a python script and where about to replace the existing rule files.

Contributor Declaration

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• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌈🌦️📖🚧 Documentation 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/multio/pull-requests/PR-186

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.61%. Comparing base (4166faa) to head (1f43047).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #186      +/-   ##
===========================================
+ Coverage    56.60%   56.61%   +0.01%     
===========================================
  Files          316      316              
  Lines        20489    20304     -185     
  Branches      1569     1569              
===========================================
- Hits         11597    11496     -101     
+ Misses        8892     8808      -84     

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[MircoValentiniECMWF]

Have you tested this change, and is it actually testable?
Please compare the generated rules against the previous JSON rules to verify consistency.
The impact of this modification appears high-risk, and the rationale behind it is not clearly explained.

[pgeier]

Have you tested this change, and is it actually testable? Please compare the generated rules against the previous JSON rules to verify consistency. The impact of this modification appears high-risk, and the rationale behind it is not clearly explained.

I compared the grib1-to-grib2 outputs from /ec/project/mdst/MDST/grib1-to-grib with grib-compare and the ERA6-LWDA dump with fdb-compare.
Both are bit identical.
The JSONs with the encoder-configurations have been invalidated with the last "hotfix" one month ago.
By that time the comparison above was already used. With the further incoming changes from the migration the JSONs can't be maintained.