Turbocharging LISTEN/NOTIFY with 40x Boost

Unless you've built a massive real-time notification system with thousands of distinct channels, it is easy to miss the quadratic performance bottleneck that Postgres used to have in its notification queue. A recent commit fixes that with a spectacular throughput improvement. The commit in question is 282b1cde9d , which landed recently and targets a future release (likely Postgres 19, though as…