refactor: Enhance docs, add more tests in `RomanToInteger`

[Hardvan]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] 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 :white_check_mark:

Project coverage is 67.21%. Comparing base (aaaf96b) to head (225f42e).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5926      +/-   ##
============================================
- Coverage     67.24%   67.21%   -0.03%     
+ Complexity     4565     4562       -3     
============================================
  Files           620      620              
  Lines         17149    17147       -2     
  Branches       3311     3309       -2     
============================================
- Hits          11531    11525       -6     
- Misses         5164     5165       +1     
- Partials        454      457       +3     

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