feat(dfir_rs): track and expose DFIR runtime metrics

[MingweiSamuel]

Tokio runtime metrics: https://docs.rs/tokio/latest/tokio/runtime/struct.RuntimeMetrics.html

Per-subgraph metrics:

• total_run_count - how many times the subgraph has been run
• total_poll_duration - amount of time the subgraph is running
• total_poll_count - how many times the subgraph is polled
• total_idle_duration - amount of time the subgraph is "idle" (not running and not complete)
• total_idle_count - how many times the subgraph is idle

Per-handoff metrics:

• total_items_count- Total items inserted into this handoff.
• ? current_items_count - Number of items currently in the handoff

[MingweiSamuel]

My comments from tracking issue #2178

Looking into how best to instrument execution of subgraphs. tokio-metrics provides comprehensive general instrumentation of async tasks, but testing using it in DFIR shows 15% longer runtime on some microbenchmarks. tokio-metrics records more properties than we care about [right now], and uses atomics and Arc to support multiple threads while we could track things directly in SubgraphData. Based on this I think it is best to implement custom instrumentation of subgraphs in DFIR with tokio-metrics as inspiration.

[MingweiSamuel]

I think we can start with a few important metrics per subgraph execution:

• total_poll_duration - amount of time the subgraph is running
• total_poll_count - how many times the subgraph is polled
• total_idle_duration - amount of time the subgraph is "idle" (not running and not complete)
• total_idle_count - how many times the subgraph is idle

[MingweiSamuel]

Some Dfir-runtime level metrics would be external events received