Module egress 

Egress worker pool for RealtimeAsync observation extraction.

Each worker receives ObsTask requests via a crossbeam channel, pins to the latest snapshot epoch, executes the observation plan, unpins, and sends the result back via a bounded(1) reply channel.

Workers allocate their own output buffers and return them via the reply channel. The caller copies into its buffer. This maintains #![forbid(unsafe_code)] at the cost of a ~10μs memcpy (negligible vs the 16.7ms tick budget).