tsp_constructive/function_description.txt

The `select_next_node` function takes as input the current node, the destination_node, a set of unvisited nodes, and a distance matrix, and returns the next node to visit.

### Solution Function Signature
```python
def select_next_node(current_node: int, destination_node: int, unvisited_nodes: set, distance_matrix: np.ndarray) -> int:
    """
    Select the next node to visit in a Traveling Salesman Problem (TSP) constructive heuristic.

    Args:
        current_node (int): The node currently being visited
        destination_node (int): The final destination node in the TSP tour
        unvisited_nodes (set): Set of nodes that haven't been visited yet
        distance_matrix (np.ndarray): NxN matrix where distance_matrix[i][j] is the distance from node i to j

    Returns:
        int: The selected next node to visit
    """
```