Use CodesHandle and refactored CodesContent in fdb-patch

[pgeier]

Description

This PR is related to ecmwf/metkit#128 - it uses the new CodesHandle directly instead of eccodes C API.

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.

🌈🌦️📖🚧 Documentation Z3FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/z3fdb/pull-requests/PR-198

🌈🌦️📖🚧 Documentation FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/fdb/pull-requests/PR-198

[simondsmart]

Looks good. very clean.

[pgeier]

Do not merge yet.
Due to the dependencies in mars-client-cpp, we need to make some more changes and create an intermediate CodesDataContent first - which will then be renamed to CodesContent in a follow up PR

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.33%. Comparing base (8abf5d2) to head (86e9648).

Files with missing lines	Patch %	Lines
src/fdb5/tools/fdb-patch.cc	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #198      +/-   ##
===========================================
+ Coverage    73.30%   73.33%   +0.03%     
===========================================
  Files          363      363              
  Lines        21956    21951       -5     
  Branches      2253     2253              
===========================================
+ Hits         16094    16097       +3     
+ Misses        5862     5854       -8     

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