test: improve coverage for core.util classes

[RoiSoleil]

This PR improves test coverage for the org.moreunit.core.util package by adding unit tests for utility classes that were previously lacking coverage.

Changes Included:

• Added LRUCacheTest to verify correct LRU eviction behavior (when entries exceed maxSize, the eldest is removed and MRU status is properly tracked).
• Added StringLengthComparatorTest to verify that strings are compared properly based on their length, covering scenarios with shorter vs longer, longer vs shorter, and equal length strings.
• Added ObjectsTest to assert behavior of utility methods equal() and hash(), including safe null handling, equal values, and hashcode generation for multiple objects.
• Added FeaturesTest to ensure feature toggle configurations based on system properties resolve correctly (true, false, default).

Validation:

• Tested classes: LRUCache, StringLengthComparator, Objects, Features.
• Covered edge cases such as null-safety (e.g. Objects.equal(null, null)), eldest eviction order when fetching cached elements, and default system property evaluation.
• Executed Maven xvfb-run -a mvn -f org.moreunit.build/pom.xml test build successfully locally with all tests passing and no regressions introduced. No mocking was required since all logic involves pure unit logic.

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PR created automatically by Jules for task 12283811644484274572 started by @RoiSoleil

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.66%. Comparing base (9145344) to head (7081005).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #348      +/-   ##
============================================
- Coverage     79.74%   79.66%   -0.08%     
+ Complexity     4058     4042      -16     
============================================
  Files           517      513       -4     
  Lines         17347    17288      -59     
  Branches       1339     1339              
============================================
- Hits          13833    13773      -60     
- Misses         2946     2947       +1     
  Partials        568      568              

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