[swayamg20]

Summary

FfiQueue.put held _lock for the whole delivery, so subscribe and unsubscribe, which every FFI request calls from its event loop, waited until the FFI callback thread had run every filter and call_soon_threadsafe.

• subscribe and unsubscribe replace the subscriber list instead of mutating it, so put iterates without _lock, as suggested in the issue
• A separate _put_lock keeps concurrent puts serialized, so every subscriber still sees events in the same order

Closes #888

Testing

• uv run pytest tests/rtc/test_ffi_queue.py tests/rtc/test_room_ffi_filter.py -q -W error
• uv run mypy livekit-protocol livekit-api livekit-rtc
• uv run ruff check . and uv run ruff format --check .

Scope

unsubscribe no longer waits for an in-flight put, so that put can still deliver its item to the removed queue.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.