Implement encoding for currently known atmospheric composition fields

[tweska]

This PR implements encoding for fields mapped in ecmwf/multio#245

[codecov-commenter]

Codecov Report

❌ Patch coverage is 7.14286% with 52 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.87%. Comparing base (0e63bba) to head (b2facd9).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../backend/concepts/composition/compositionMatcher.h	12.90%	27 Missing ⚠️
...backend/concepts/composition/compositionEncoding.h	0.00%	9 Missing ⚠️
...kit/mars2grib/backend/deductions/firstWavelength.h	0.00%	8 Missing ⚠️
src/metkit/mars2grib/backend/deductions/chemId.h	0.00%	4 Missing ⚠️
...it/mars2grib/backend/concepts/level/levelMatcher.h	0.00%	3 Missing ⚠️
...ackend/concepts/point-in-time/pointInTimeMatcher.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #184      +/-   ##
===========================================
- Coverage    62.06%   61.87%   -0.20%     
===========================================
  Files          303      304       +1     
  Lines        11710    11750      +40     
  Branches      1052     1051       -1     
===========================================
+ Hits          7268     7270       +2     
- Misses        4442     4480      +38     

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[tweska]

I seem to have broken something with this PR. I'll keep this as draft until I figure out what.

It was a ) in the wrong position... :^/

[MircoValentiniECMWF]

Now seems ok. Thanks