feat(deepgram): use Configure control message for mid-stream keyterm updates

[Panmax]

Summary

• When only keyterm, EOT thresholds, or language_hint are updated via update_options(), send a Deepgram Configure control message instead of reconnecting the WebSocket
• This avoids dropping in-progress speech recognition when options change mid-stream (e.g. updating keyterms while the user is speaking)
• Options that cannot be updated mid-stream (model, sample_rate, mip_opt_out, endpoint_url, tags) still trigger a full reconnect as before

Motivation

Currently, any call to SpeechStreamv2.update_options() triggers _reconnect_event.set(), which tears down the active WebSocket and reconnects. If this happens while the user is speaking, any in-progress INTERIM_TRANSCRIPT is lost and the final transcript may be incomplete.

Deepgram's Flux models support a Configure control message that allows updating keyterms, EOT thresholds, and language hints mid-stream without reconnecting:

{
  "type": "Configure",
  "keyterms": ["term1", "term2"],
  "thresholds": {
    "eot_threshold": 0.8,
    "eot_timeout_ms": 5000
  }
}

Ref: https://developers.deepgram.com/docs/flux/configure#configure-message

Changes

• Added self._ws instance variable to SpeechStreamv2 to hold the current WebSocket reference
• Added _send_configure() method that constructs and sends the Configure control message
• Modified update_options() to check whether the update requires a reconnect or can be applied mid-stream via Configure message
• Handle ConfigureSuccess / ConfigureFailure responses from Deepgram — on failure, fall back to reconnect so options still take effect
• Use asyncio.create_task with tracked reference instead of fire-and-forget ensure_future; cancel pending task on WebSocket cleanup
• Fall back to reconnect if Configure message send fails (e.g. WebSocket closing concurrently)

Test plan

• Verify keyterm updates via Configure message don't interrupt ongoing speech recognition
• Verify EOT threshold updates via Configure message work correctly
• Verify model/sample_rate/endpoint changes still trigger reconnect
• Verify behavior when WebSocket is not yet connected (falls back to reconnect)
• Verify ConfigureFailure triggers reconnect and logs warning
• Verify send failure (e.g. ws closed mid-send) falls back to reconnect

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