feat: add webhook support to streaming parameters

[dylan-duan-aai]

Summary

• Add webhook_url, webhook_auth_header_name, and webhook_auth_header_value fields to StreamingParameters
• These are passed as query params on the WebSocket URL, enabling server-side webhook delivery of the transcript when a streaming session ends
• Docs: https://assemblyai-preview-6804fd2c-e8bf-4886-8dbc-b94c49176ae1.docs.buildwithfern.com/docs/deployment/webhooks-for-streaming-speech-to-text

Changes

• assemblyai/streaming/v3/models.py — 3 new optional fields on StreamingParameters
• tests/unit/test_streaming.py — new test_client_connect_with_webhook test

Test plan

• Unit test verifies webhook params appear in the WebSocket URL query string
• All 5 streaming tests pass

[dylan-duan-aai]

moving to deeplearning