test: improve coverage for core module classes

[RoiSoleil]

Added new tests and expanded existing test cases in the org.moreunit.core module to improve JaCoCo test coverage, specifically targeting unhandled conditions in NullDialog, TestJumper, NameTokenizerTestCase, and Language.

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PR created automatically by Jules for task 18181509042702420647 started by @RoiSoleil

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[codecov]

Codecov Report

❌ Patch coverage is 81.94444% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.35%. Comparing base (fba087f) to head (f5574b5).

Files with missing lines	Patch %	Lines
...eunit/core/matching/NameTokenizerTestCaseTest.java	64.51%	6 Missing and 5 partials ⚠️
...test/org/moreunit/core/languages/LanguageTest.java	93.93%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #285      +/-   ##
============================================
+ Coverage     75.21%   75.35%   +0.14%     
- Complexity     3324     3344      +20     
============================================
  Files           423      425       +2     
  Lines         14605    14677      +72     
  Branches       1271     1278       +7     
============================================
+ Hits          10985    11060      +75     
+ Misses         3088     3083       -5     
- Partials        532      534       +2     

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