[Speech Engine] Add disable_auth parameter

[PaulAsjes]

Adds new disable_auth parameter.

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Note

High Risk
Opt-out JWT verification on the Speech Engine WebSocket entrypoint is security-sensitive; misuse exposes sessions to unauthenticated clients and downstream LLM/compute abuse, though the flag defaults off and is documented as insecure.

Overview
Adds an opt-in disable_auth flag on SpeechEngineServer and SpeechEngineResource.serve() so deployments behind an ElevenLabs IP allowlist can skip JWT checks on X-Elevenlabs-Speech-Engine-Authorization. With auth disabled, an API key is no longer required at startup, the handshake bypasses verification, and a UserWarning is emitted; default behavior still rejects missing or invalid JWTs with 401.

The standalone server now uses websockets.asyncio.server.serve (dependency bumped to websockets>=13.0) so the process_request hook matches the asyncio (connection, request) / connection.respond() API. Release 2.56.0 and README Authentication docs accompany the change, plus integration tests for disabled auth, warnings, and enforced auth paths.

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[anitej-11]

lgtm, thanks!