Add Topological Sort algorithm using DFS in GraphSearch

[Saipatnaik-23]

Description

This PR adds an implementation of Topological Sort using Depth-First Search (DFS) in Java under com.thealgorithms.graphsearch .

• ✅ Uses DFS approach
• ✅ Handles Directed Acyclic Graph (DAG)
• ✅ Includes inline documentation and Javadoc comments
• ✅ Includes a sample test case in main

Checklist

• 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

let me know if improvements are needed. 😊

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.06%. Comparing base (7602f1e) to head (2c80f84).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6263      +/-   ##
============================================
- Coverage     74.07%   74.06%   -0.01%     
+ Complexity     5351     5350       -1     
============================================
  Files           677      677              
  Lines         18648    18648              
  Branches       3621     3621              
============================================
- Hits          13813    13812       -1     
  Misses         4276     4276              
- Partials        559      560       +1     

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[Saipatnaik-23]

Hello maintainers! This PR is ready for review — all checks are passing. Please let me know if any changes are needed. Thank you! 😊

[DenizAltunkapan]

Isn't the topological sorting already implemented in src/main/java/com/thealgorithms/sorts/TopologicalSort.java ?

[Saipatnaik-23]

Oh You're right — I overlooked that it's already implemented in the sorts directory. Thanks for pointing that out.
Would you prefer that I close this PR, or is there a way I could contribute/improve the existing implementation?

[DenizAltunkapan]

The existing implementation in com.thealgorithms.sorts.TopologicalSort is already a robust.

If you'd like to contribute, a great way would be to add unit tests for that class in the existing test suite or look into possible performance optimizations. @Saipatnaik-23

[DenizAltunkapan]

@siriak what's your opinion on this one?

[DenizAltunkapan]

The existing implementation in com.thealgorithms.sorts.TopologicalSort is already a robust.

If you'd like to contribute, a great way would be to add unit tests for that class in the existing test suite or look into possible performance optimizations. @Saipatnaik-23

[Saipatnaik-23]

Hello @DenizAltunkapan Added new test cases for empty and single-node graphs in the existing src/main/java/com/thealgorithms/sorts/TopologicalSort.java . Please review. Thanks!