feat(rtc): add restart_publisher method to Room

[Hormold]

Summary

• Add restart_publisher() method stub to the Room class
• The method currently raises NotImplementedError as a placeholder until FFI bindings are added to rust-sdks

Motivation

When using the Python SDK for real-time meeting applications, we encountered a scenario where:

1. The publisher PeerConnection gets stuck (ICE connection fails)
2. The subscriber PeerConnection continues working normally
3. Audio/video receiving works fine
4. But sending data via stream_text(), publish_data(), etc. times out

Currently, there's no way to recover from this state without disconnecting the entire room, which breaks the audio streams.

The Rust SDK already has restart_publisher() at the engine level (in rtc_session.rs):

async fn restart_publisher(&self) -> EngineResult<()> {
    if self.has_published.load(Ordering::Acquire) {
        self.publisher_pc
            .create_and_send_offer(OfferOptions { ice_restart: true, ..Default::default() })
            .await?;
    }
    Ok(())
}

This PR adds a placeholder method that will be fully implemented once the FFI bindings are added.

Usage (Future)

try:
    await room.local_participant.publish_data(data)
except TimeoutError:
    # Publisher might be stuck, try to restart it
    await room.restart_publisher()
    # Retry the operation
    await room.local_participant.publish_data(data)

Implementation Status

This is a stub implementation that raises NotImplementedError:

async def restart_publisher(self) -> None:
    raise NotImplementedError(
        "restart_publisher() requires FFI bindings in livekit/rust-sdks. "
        "This is a placeholder for future implementation."
    )

Next Steps

To fully implement this feature:

1. Add FFI bindings in livekit/rust-sdks:
   • RestartPublisherRequest, RestartPublisherResponse, RestartPublisherCallback in room.proto
   • Handler in requests.rs
   • Expose restart_publisher() on Room and RtcEngine
2. Update the python-sdks submodule
3. Replace the stub with the actual FFI call implementation

Test Plan

• Method exists and is documented
• Full implementation pending rust-sdks FFI bindings

🤖 Generated with Claude Code