Do not allow anymore to create Variables or Attributes with an empty name

[jeandet]

This pull request introduces input validation to ensure that variable and attribute names cannot be empty throughout the CDF library, improving data integrity and preventing subtle bugs. It also adds corresponding Python unit tests to verify these constraints. Additionally, the pull request includes a minor improvement to the variable output streaming function.

Input validation improvements:

• Added checks in the constructors of Variable, Attribute, and VariableAttribute (in variable.hpp and attribute.hpp) to throw an exception if the name is empty, enforcing that all variable and attribute names must be non-empty. [1] [2] [3] [4]

Testing enhancements:

• Added a new Python test class (PycdfEmptyNamesAreNotAllowed in test.py) that verifies an exception is raised when attempting to create variables or attributes with empty names, ensuring the new validation logic is covered.

Code maintainability:

• Improved the operator<< for cdf_map<std::string, cdf::Variable> in cdf-file.hpp by using std::for_each for cleaner and more modern iteration over variables.

Closes #48

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.18%. Comparing base (4edf261) to head (49fb44c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
include/cdfpp/cdf-file.hpp	0.00%	1 Missing ⚠️
include/cdfpp/variable.hpp	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
- Coverage   88.27%   88.18%   -0.09%     
==========================================
  Files          56       56              
  Lines        3198     3209      +11     
==========================================
+ Hits         2823     2830       +7     
- Misses        375      379       +4     

Flag	Coverage Δ
unittests	88.18% <77.77%> (-0.09%)	⬇️

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