refactor: refactoring and documenting Isomorphic String Checker

[alxkm]

This PR improves the Isomorphic utility class by enhancing readability, renaming variables and methods for clarity, and adding full Javadoc documentation.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.64%. Comparing base (2ccc156) to head (37a174a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6359      +/-   ##
============================================
- Coverage     74.64%   74.64%   -0.01%     
+ Complexity     5451     5450       -1     
============================================
  Files           682      682              
  Lines         19013    19015       +2     
  Branches       3673     3673              
============================================
+ Hits          14192    14193       +1     
  Misses         4262     4262              
- Partials        559      560       +1     

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