DGOV-649 Add support for subtype 58

[Manuel-Fuentes]

Description

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.

📋 Metkit Documentation 📋
https://sites.ecmwf.int/docs/metkit/pull-requests/PR-241

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.51%. Comparing base (ab98831) to head (8ecbd6c).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #241   +/-   ##
========================================
  Coverage    50.51%   50.51%           
========================================
  Files          385      385           
  Lines        15438    15438           
  Branches      1307     1307           
========================================
  Hits          7798     7798           
  Misses        7640     7640           

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[danovaro]

lgtm, thanks @Manuel-Fuentes