Improve hybrid level handling

[sandorkertesz]

Description

Improves the code writing Field hybrid level information into GRIB.

Contributor Declaration

By opening this pull request, I affirm the following:

• 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.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.42%. Comparing base (320c4b6) to head (bce4868).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1040   +/-   ##
========================================
  Coverage    82.41%   82.42%           
========================================
  Files          237      237           
  Lines        16721    16730    +9     
  Branches       813      813           
========================================
+ Hits         13780    13789    +9     
  Misses        2699     2699           
  Partials       242      242           

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