fix(graph): return ordered cycle path and add early exit in detectUndirectedCycle

[punit1009]

Summary

This fixes issue #2057 .

The detectUndirectedCycle function previously returned a vertex-to-parent mapping which was unintuitive and difficult to consume. This PR changes the function to return an ordered array of vertices forming the cycle (e.g. [A, B, C, A]), with the first and last elements equal to clearly indicate the cycle closure.

Changes

• Return ordered cycle path array instead of object map.
• Add early exit (stop traversal once a cycle is found).
• Ensure function iterates all graph components (handles disconnected graphs).
• Add unit tests to verify behavior and maintain 100% coverage.

Checklist

• Code matches repository style
• npm run lint passes (or auto-fixed)
• npm test passes
• 100% test coverage for modified files

Fixes #123

[asanpardazzagros-debug]

@trekhleb @punit1009