refactor: Enhance docs, remove `main`. add more tests in `IntegerToRo…

[Hardvan]

…man`

• [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 67.98%. Comparing base (0feb416) to head (d9c5423).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5925      +/-   ##
============================================
+ Coverage     67.97%   67.98%   +0.01%     
+ Complexity     4587     4586       -1     
============================================
  Files           620      620              
  Lines         17119    17116       -3     
  Branches       3306     3305       -1     
============================================
  Hits          11637    11637              
+ Misses         5037     5034       -3     
  Partials        445      445              

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