Implement cloneGraph method to deep copy an undirected graph

[cd155]

This pull request implements the solution for cloning an undirected graph in the cloneGraph method of the Solution class. The method now uses a depth-first search (DFS) approach with a hashmap to track visited nodes, ensuring that each node is cloned only once and that cycles are handled correctly.

Implementation of graph cloning:

• Replaced the placeholder implementation in cloneGraph with a working DFS-based solution that clones the graph, using a visited dictionary to avoid duplicating nodes and to handle cycles.
• Renamed the method parameter from node to source for clarity and consistency throughout the method.

[Copilot]

Pull request overview

This PR implements a DFS-based deep copy for LeetCode 133 (“Clone Graph”) in Solution.cloneGraph, using a visited map to avoid duplicating nodes and to handle cycles.

Changes:

• Implemented cloneGraph using DFS recursion and a visited dictionary for memoization.
• Renamed the cloneGraph parameter from node to source.

Comments suppressed due to low confidence (1)

src/graph/clone_graph.py:36

• The docstring still documents the argument as node, but the method parameter was renamed to source. Update the Args: section to match (source: Node - reference to a node in the graph) to avoid misleading readers and tooling.

    def cloneGraph(self, source):
        """
        Clone an undirected graph.

        Args:
            node: Node - reference to a node in the graph

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

For an empty input graph, this returns None (via bare return). The docstring currently says the method returns Node - cloned graph; please clarify in the Returns: section that None is returned when source is None (or explicitly return None for clarity).