Function find_paths 

pub(crate) fn find_paths<C>(
    inner: &InnerGraph,
    source: NodeIndex,
    destinations: &HashSet<NodeIndex>,
    length: usize,
    take_count: Option<usize>,
    initial_cost: C,
    min_cost: Option<C>,
    cost_fn: Arc<dyn Fn(C, &Observations, usize) -> C + Send + Sync>,
) -> Vec<(Vec<OffchainPublicKey>, PathId, C)>
where
    C: Clone + PartialOrd,

Core path-finding routine that runs all_simple_paths_multi on the inner petgraph.