Tidy up and read through src/GDXFile.jl

[odow]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.21%. Comparing base (7924d7d) to head (556b5e9).

Files with missing lines	Patch %	Lines
src/gdx_c_api.jl	33.33%	6 Missing ⚠️
src/GDXFile.jl	87.80%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
- Coverage   87.85%   87.21%   -0.65%     
==========================================
  Files           3        3              
  Lines         593      618      +25     
==========================================
+ Hits          521      539      +18     
- Misses         72       79       +7     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.