refactor: BoardPath

[alxkm]

Class cleanup.
Readability improvements.
Added tests.

• 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 50.97%. Comparing base (c5b7281) to head (05503b9).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5431      +/-   ##
============================================
+ Coverage     50.78%   50.97%   +0.18%     
- Complexity     3138     3152      +14     
============================================
  Files           523      523              
  Lines         15108    15104       -4     
  Branches       2874     2874              
============================================
+ Hits           7673     7699      +26     
+ Misses         7114     7084      -30     
  Partials        321      321              

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