Optimize BFS and fix min-cut detection in Ford-Fulkerson algorithm

[Vishnunair585]

Changes made

• Replaced list queue with deque for O(1) pop
• Added early exit in BFS when sink is found
• Preserved original graph using residual copy
• Fixed min-cut detection using DFS on residual graph
• Returned max_flow along with min-cut edges

[algorithms-keeper]

Closing this pull request as invalid

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