Refactor UnionFind

[sozelfist]

Checklist ☑️

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.02%. Comparing base (4e59645) to head (433d003).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #729      +/-   ##
==========================================
+ Coverage   94.95%   95.02%   +0.07%     
==========================================
  Files         303      303              
  Lines       22533    22579      +46     
==========================================
+ Hits        21396    21456      +60     
+ Misses       1137     1123      -14     

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