refactor: Enhance docs, remove `main`, add tests in `PrimMST`

[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 72.30%. Comparing base (ce3dd01) to head (071b5f0).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5969      +/-   ##
============================================
+ Coverage     72.12%   72.30%   +0.18%     
- Complexity     4944     4956      +12     
============================================
  Files           650      650              
  Lines         17555    17546       -9     
  Branches       3384     3383       -1     
============================================
+ Hits          12661    12687      +26     
+ Misses         4416     4382      -34     
+ Partials        478      477       -1     

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