Fix broadcast screen share hanging without frames

[pblazej]

When the automatic screen share publish failed, the broadcast extension kept retrying against a socket with no listener, so the broadcast came up without frames.

• Publish: _publish checked permissions before the publisher, and a disconnected room resets the local participant's permissions, so it failed as Unknown(Participant does not have permission to publish); it now checks the publisher first, stops the broadcast on failure, and every LiveKitErrorType has a description.
• IPC: the listener treats .waiting as transient, reconnects every 100 ms instead of busy-looping (UInt64(0.1) truncated the delay to zero), and copies the shared NWParameters so concurrent listeners stop binding each other's paths, which also de-flakes IPCChannelTests.
• Capturer: stopping before the extension connects now cancels the waiting listener instead of leaking the capturer, and a second active broadcast capturer (e.g. two connected rooms) logs a warning, since only one of them can receive the broadcast.

Network.framework is not the cause: the SO_NECP_LISTENUUID warnings also appear in successful runs.

Fixes: #1132

[xianshijing-lk]

some questions

[xianshijing-lk]

can createReceiver() be called more than once ?

any chance that it will overwrite existing receiverTask without cancelling it or decrementing activeCount ?

[pblazej]

7ad6da8

[xianshijing-lk]

should activeCount track the task lifetime ? rather than task creation ?

If it is for task lifetime, I wonder if we should do

receiverTask = Task { [weak self] in
    Self.activeCount.mutate { $0 += 1 }

    defer {
        Self.activeCount.mutate { $0 -= 1 }
    }

    await self?.receive(from: socketPath)
}.cancellable()

[pblazej]

7ad6da8