METK-144 Replace & Remove GribHandle

[pgeier]

Description

This PR removes the usage of metkit/GribHandle everywhere possible in favor of new CodesHandle.
Fully removal will change once subsequent PRs using old CodesHandle have been merged.

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 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.10%. Comparing base (7094899) to head (cad1926).

Files with missing lines	Patch %	Lines
src/metkit/pointdb/PointIndex.cc	0.00%	16 Missing ⚠️
src/metkit/pointdb/GribFieldInfo.cc	0.00%	12 Missing ⚠️
src/metkit/pointdb/GribHandleDataSource.cc	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #153      +/-   ##
===========================================
+ Coverage    59.10%   60.10%   +1.00%     
===========================================
  Files          309      302       -7     
  Lines        11671    11376     -295     
  Branches      1022     1011      -11     
===========================================
- Hits          6898     6838      -60     
+ Misses        4773     4538     -235     

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