code: def all_neighbour_nodes(chain_state: ChainState) -> Set[Address]:
      
      addresses = set()
  
      for payment_network in chain_state.identifiers_to_paymentnetworks.values():
          for token_network in payment_network.tokenidentifiers_to_tokennetworks.values():
              channel_states = token_network.channelidentifiers_to_channels.values()
              for channel_state in channel_states:
                  addresses.add(channel_state.partner_state.address)
  
      return addresses
docs: Return the identifiers for all nodes accross all payment networks which
      have a channel open with this one.