Clone Graph

Given a reference to a node in a connected, undirected graph, return a deep copy of the graph. Each node contains a value (int) and a list of its neighbors (List[Node]).

Input/output convention for this exercise. The graph is supplied as a 1-indexed adjacency list — adjList[i] lists the 1-indexed labels of the i+1-th node's neighbors. For example, [[2,4],[1,3],[2,4],[1,3]] describes a 4-node graph where node 1's neighbors are nodes 2 and 4, etc.

To verify that you actually deep-copied the graph (rather than returning the original references), your function must:

1. Build the graph from the adjacency list (the starter provides buildGraph and Node).
2. Clone it.
3. Re-serialize the clone via the provided serializeGraph helper, which returns the adjacency list of whatever graph it walks. Return that.

The result should equal the input adjacency list when the clone is correct. The graph is guaranteed connected (LeetCode 133), so disconnected inputs are out of scope.

Empty input [] represents the empty graph; return [].