Add topological sorting using Khan's algorithm

[thejeswar2419]

Kahn’s Algorithm provides a clear and efficient way to perform topological ordering while also offering built-in cycle detection and avoiding recursion-depth issues.

[keon]

Thanks for the contribution! We already have Kahn's algorithm in algorithms/graph/kahns_algorithm.py and topological sort variants in topological_sort_bfs.py / topological_sort_dfs.py. Closing as duplicate.