feat(barge-in): add default threshold support and drop http transport

[chenghao-mou]

Backport of #1698 (originally merged into the 1.5.0 branch) to main.

Cherry-picks 416871a5:

• Adds default threshold support for barge-in / adaptive interruption.
• Drops the HTTP transport for interruption (http_transport.ts), standardizing on the WS transport; adds _mock_ws.ts plus failover / session-create tests.

Clean cherry-pick onto main (no conflicts). No public export surface change. Changeset bargein-default-threshold-drop-http.md carried over.

Note: the matching change is also present on the EOU branch (#1719) which still edits http_transport.ts. Whichever of the two lands on main second will need to resolve the resulting modify/delete on that file.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 016685f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 35 packages

Name	Type
@livekit/agents	Patch
@livekit/agents-plugin-anam	Patch
@livekit/agents-plugin-assemblyai	Patch
@livekit/agents-plugin-baseten	Patch
@livekit/agents-plugin-bey	Patch
@livekit/agents-plugin-cartesia	Patch
@livekit/agents-plugin-cerebras	Patch
@livekit/agents-plugin-deepgram	Patch
@livekit/agents-plugin-did	Patch
@livekit/agents-plugin-elevenlabs	Patch
@livekit/agents-plugin-fishaudio	Patch
@livekit/agents-plugin-google	Patch
@livekit/agents-plugin-hedra	Patch
@livekit/agents-plugin-hume	Patch
@livekit/agents-plugin-inworld	Patch
@livekit/agents-plugin-lemonslice	Patch
@livekit/agents-plugin-liveavatar	Patch
@livekit/agents-plugin-livekit	Patch
@livekit/agents-plugin-minimax	Patch
@livekit/agents-plugin-mistral	Patch
@livekit/agents-plugin-mistralai	Patch
@livekit/agents-plugin-neuphonic	Patch
@livekit/agents-plugin-openai	Patch
@livekit/agents-plugin-perplexity	Patch
@livekit/agents-plugin-phonic	Patch
@livekit/agents-plugin-resemble	Patch
@livekit/agents-plugin-rime	Patch
@livekit/agents-plugin-runway	Patch
@livekit/agents-plugin-sarvam	Patch
@livekit/agents-plugin-silero	Patch
@livekit/agents-plugin-soniox	Patch
@livekit/agents-plugin-tavus	Patch
@livekit/agents-plugins-test	Patch
@livekit/agents-plugin-trugen	Patch
@livekit/agents-plugin-xai	Patch

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[devin-ai-integration]

Devin Review found 1 potential issue.