voice: voice.adapter.disconnect span lands on a detached trace id, not the scenario's trace

[drewdrewthis]

The disconnect span (which carries voice.twilio.stream_ended_reason, frames_received, speech_gate.* counters) is emitted after the scenario trace has ended and is exported under its own trace id (dev run scenariorun_0007chJwsufAHGUoXsb63INYosdUr: run trace 177f9a07651f86653cd54c9de7b1077c, disconnect span on 549381b74304063610e5180e37d4805d, 15 s after the verdict). All 77 disconnect spans on the dev stack behave the same.

Proposal: capture the run's trace context at connect and start the disconnect span under it (or stamp the counters on the last adapter call span).

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