test: improve coverage for utility classes

[RoiSoleil]

• Added comprehensive unit tests for StringConstants to verify constant values.
• Added comprehensive unit tests for ExtendedSafeRunner to verify single element execution, iterable execution, and exception handling paths.
• These tests use standard JUnit 5 and AssertJ, avoiding unnecessary mocking frameworks or OSGi dependencies.
• Verified that the test suite runs successfully with these new tests.

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PR created automatically by Jules for task 12754723206302569238 started by @RoiSoleil

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.67%. Comparing base (fe5579f) to head (d9d5219).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #349      +/-   ##
============================================
- Coverage     79.67%   79.67%   -0.01%     
+ Complexity     4042     4038       -4     
============================================
  Files           513      511       -2     
  Lines         17288    17258      -30     
  Branches       1339     1339              
============================================
- Hits          13774    13750      -24     
+ Misses         2947     2943       -4     
+ Partials        567      565       -2     

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