Cascade close and select on group.closed() in subscribers

[kixelated]

Summary

• Add Producer::closed() / GroupProducer::closed() to await explicit state closure
• Add TrackWeak::close() that cascades close to all child groups
• Update BroadcastProducer::close() to cascade to child tracks and pending requests
• Add select! on group.closed() in both lite and IETF subscriber recv_group, so we stop reading from the QUIC stream when the group is closed (e.g. due to subscription cancellation)

Test plan

• All 149 moq-lite tests pass (including updated broadcast cascade test)
• just check passes
• Manual testing with live streams to verify subscriptions are cleaned up promptly

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 20c0cfe and b24449f.

📒 Files selected for processing (6)

• rs/moq-lite/src/ietf/subscriber.rs
• rs/moq-lite/src/lite/subscriber.rs
• rs/moq-lite/src/model/broadcast.rs
• rs/moq-lite/src/model/group.rs
• rs/moq-lite/src/model/state.rs
• rs/moq-lite/src/model/track.rs

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Walkthrough

This pull request introduces concurrency improvements and error cascading through the broadcast hierarchy. The subscriber modules now use tokio::select! to race between producer closure and group task completion instead of awaiting directly. The run_group method signature changes to accept an owned GroupProducer. New closed() async methods are added to GroupProducer and Producer<T> with backing implementation in the state layer. BroadcastProducer::close now cascades errors to all child tracks and pending dynamic track requests. A new close(err) method is added to TrackWeak to propagate errors upward through associated groups.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 13.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Cascade close and select on group.closed() in subscribers' directly describes the main changes: cascading close operations and adding select! on group.closed() in subscriber code.
Description check	✅ Passed	The description is well-aligned with the changeset, detailing the new Producer/GroupProducer closed() methods, TrackWeak::close() cascade behavior, and subscriber select! changes.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch verify-unsub

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