test: cleanup PrimeFactorizationTest

[alxkm]

Class cleanup.
Readability improvements.
Added more test cases.

• 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 46.91%. Comparing base (3868844) to head (6cad7ce).
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5382      +/-   ##
============================================
+ Coverage     46.90%   46.91%   +0.01%     
- Complexity     2903     2904       +1     
============================================
  Files           525      525              
  Lines         15364    15364              
  Branches       2908     2908              
============================================
+ Hits           7206     7208       +2     
+ Misses         7856     7855       -1     
+ Partials        302      301       -1     

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