Measure in-flight writes alongside completed-write latency

When diagnosing an asynchronous WebSocket stall, record the active write phase and its current elapsed time alongside completed-write latency, lock-wait time and queued bytes. A maximum updated only after a send finishes excludes the operation that is currently blocked; apparently fast historical writes therefore cannot establish a healthy current writer. Distinguish waiting for the application lock from awaiting the socket, and preserve the observation before cleanup changes state. These are local progress measurements: even a completed send does not prove provider consumption, playback, or which network component stalled.

Applies when: A bounded audio or message queue fills while completed-operation latency still appears healthy. Keywords: asyncio WebSocket pending write latency telemetry queue backpressure timeout