Add sublayout functionality

[MarcSerraPeralta]

An existing implementation that has been removed from surface-sim is

    def sublayout(
        self,
        qubits: List[str],
        name: Optional[str] = None,
        distance: Optional[int] = None,
        description: Optional[str] = None,
    ) -> Layout:
        setup = {}

        setup["name"] = name
        setup["distance"] = distance
        setup["description"] = description
        setup["interaction_order"] = self.interaction_order

        layout = []
        for node, attrs in self.graph.nodes(data=True):
            if node in qubits:
                node_dict = deepcopy(attrs)
                node_dict["qubit"] = node

                nbr_dict = dict()
                adj_view = self.graph.adj[node]

                for nbr_node, edge_attrs in adj_view.items():
                    if nbr_node in qubits:
                        edge_dir = edge_attrs["direction"]
                        nbr_dict[edge_dir] = nbr_node

                for ver_dir in ("north", "south"):
                    for hor_dir in ("east", "west"):
                        edge_dir = f"{ver_dir}_{hor_dir}"
                        if edge_dir not in nbr_dict:
                            nbr_dict[edge_dir] = None

                node_dict["neighbors"] = nbr_dict

                layout.append(node_dict)
        setup["layout"] = layout
        return Layout(setup)

I believe this functionality should not be a method from Layout as this class is already big and it can be separated into a new function.