METK-143 Extend CodesAPI with message data and offset calls

[pgeier]

Description

This PR extends the CodesHandle with additional calls provided by the eccodes API.
Added calls: messageData, messageOffset.

The calls are needed in preparation to rework the CodesContent #128

As the calls are just adding feature, no bad effects are expected at other places.

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

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.03%. Comparing base (908e6ff) to head (e89c72c).

Files with missing lines	Patch %	Lines
src/metkit/codes/api/CodesAPI.cc	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #147      +/-   ##
===========================================
- Coverage    71.07%   71.03%   -0.05%     
===========================================
  Files          130      130              
  Lines         8160     8165       +5     
  Branches       781      781              
===========================================
  Hits          5800     5800              
- Misses        2360     2365       +5     

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