/// this, MPP will only be used if the payee's features are available in the network graph.
///
/// Private routing paths between a public node and the target may be included in `payee`.
-/// Currently, only the last hop in each path is considered.
///
/// If some channels aren't announced, it may be useful to fill in a first_hops with the
/// results from a local ChannelManager::list_usable_channels() call. If it is filled in, our