Add Topological sorting algorithm and test script

[codomposer]

Summary

This PR adds Topological Sort algorithm implementation to the Graph algorithms collection. Topological Sort is a fundamental graph algorithm that produces a linear ordering of vertices in a Directed Acyclic Graph (DAG) such that for every directed edge (u, v), vertex u comes before vertex v in the ordering.

Motivation and Context

Topological Sort is a well-established algorithm from reputable academic sources including:

• "Introduction to Algorithms" (CLRS) by Cormen, Leiserson, Rivest, and Stein
• "Algorithm Design Manual" by Steven Skiena

This algorithm was notably missing from the repository's graph algorithms collection and is essential for:

• Build systems: Compile dependencies in correct order
• Task scheduling: Execute tasks respecting dependencies
• Course prerequisites: Order courses based on requirements
• Package dependency resolution: Resolve dependency chains

Implementation Details

• Two algorithm approaches:
  1. DFS-based: Uses depth-first search with post-order traversal
  2. Kahn's Algorithm: Uses in-degree counting and BFS-based processing
• Time Complexity: O(V + E) for both approaches
• Space Complexity: O(V)
• Cycle Detection: Both methods detect cycles and throw appropriate exceptions for non-DAG graphs
• Comprehensive documentation: Detailed inline comments explaining algorithm steps and concepts

Testing

• Added 18 comprehensive test cases covering:
  • Simple linear graphs
  • Complex DAGs with multiple valid orderings
  • Disconnected graphs
  • Cycle detection (including self-loops)
  • Real-world scenarios (course prerequisites)
  • Single vertex graphs
  • Different data types (string and integer vertices)
• All tests pass successfully ✅

Files Changed

• Algorithms/Graph/TopologicalSort.cs - Algorithm implementation (290 lines)
• Algorithms.Tests/Graph/TopologicalSortTests.cs - Comprehensive tests (573 lines)
• README.md - Updated to include link to Topological Sort

Checklist

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

Contribution by Gittensor, learn more at https://gittensor.io/

[codecov]

Codecov Report

❌ Patch coverage is 97.47899% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.89%. Comparing base (5bcbece) to head (19b9a64).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
Algorithms/Graph/TopologicalSort.cs	97.47%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #564    +/-   ##
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  Coverage   96.89%   96.89%            
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  Files         291      292     +1     
  Lines       12035    12154   +119     
  Branches     1740     1761    +21     
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+ Hits        11661    11777   +116     
- Misses        237      239     +2     
- Partials      137      138     +1     

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[siriak]

Looks good, thanks!