Function streaming_bfs 

pub fn streaming_bfs(
    stream: &mut GraphStream,
    config: &StreamingBfsConfig,
) -> StreamBfsResult

Memory-efficient multi-pass BFS over a GraphStream.

Because a streaming BFS cannot rewind the stream, we work over a snapshot of edges (the stream is fully consumed once and stored as an edge list). Pass k discovers all vertices at distance k from the source. Only the current frontier and the visited set need to be kept in memory.

Algorithm

1. Consume the stream into an edge list (required for multi-pass).
2. Pass 0: initialise visited = {source}, frontier = {source}, dist[source] = 0.
3. Pass k: scan every edge; if exactly one endpoint is in the frontier and the other is unvisited, add the other to the next frontier at distance k+1.
4. Repeat until no new vertices are discovered or max_dist is reached.