feat: Added topological sort using DFS

[mjk22071998]

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• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
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[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.65217% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.16%. Comparing base (14a23b7) to head (397e9a9).

Files with missing lines	Patch %	Lines
...ithms/datastructures/trees/BinaryTreeToString.java	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6757      +/-   ##
============================================
+ Coverage     77.11%   77.16%   +0.04%     
- Complexity     6111     6130      +19     
============================================
  Files           719      721       +2     
  Lines         20437    20483      +46     
  Branches       3952     3962      +10     
============================================
+ Hits          15761    15805      +44     
- Misses         4079     4080       +1     
- Partials        597      598       +1     

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