Function format_dag_explain 

pub fn format_dag_explain(dag: &StreamingDag) -> DagExplainOutput

Formats a DAG topology into an EXPLAIN DAG output.

Example output

DAG Topology (5 nodes, 4 edges)
================================
Sources: [trades]
Execution order: trades -> ohlc_1s -> ohlc_1m -> vwap, anomaly
Shared stages: ohlc_1s (2 consumers)
Channel types:
  trades -> ohlc_1s: SPSC
  ohlc_1s -> vwap: SPMC
  ohlc_1s -> anomaly: SPMC