Increase test coverage

[sawom666]

Description

Add a test to ensure the function "build" in src/eccodes/CodesFactory.h is fully covered.

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.

[sawom666]

I also noticed the following file is not used:
eccodes/src/eccodes/AccessorFactory.h
and can be removed

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.22%. Comparing base (4a61c80) to head (96f42ed).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #500      +/-   ##
===========================================
+ Coverage    88.16%   88.22%   +0.06%     
===========================================
  Files          854      854              
  Lines        63582    63582              
  Branches     11301    11301              
===========================================
+ Hits         56056    56096      +40     
+ Misses        7526     7486      -40     

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[sawom666]

Here are the improvements:
Change in coverage:
third_party/expected/include/tl/expected.hpp 2.22%
src/eccodes/CodesFactory.h 47.22%
src/eccodes/grib_handle.cc 0.37%
src/eccodes/string_util.cc 10.42%
src/eccodes/ExceptionHandler.h 9.09%