Highlights:
- BufferedReassembler::with_max_buffer + OverflowPolicy
  (SlidingWindow / DropFlow).
- FlowStats reassembly diagnostics on every Ended event.
- Live FlowEvent::Anomaly stream (opt-in via with_emit_anomalies).
- FlowSessionDriver — sync mirror of netring's session_stream.
- Optional metrics + tracing features (zero-cost when off).
- Hot-cache fast path on FlowTracker.

Breaking:
- #[non_exhaustive] applied to FlowStats / FlowTrackerConfig /
  AnomalyKind / OverflowPolicy.
- FlowEvent::key() now returns Option<&K> (was &K).
- EndReason gained BufferOverflow variant.
- Reassembler trait gained three default-zero diagnostic methods.

See CHANGELOG.md for the full release notes and migration recipes.