additional for #1101 - make sure the queue gets marked as completed when unsubscribing; simplify the way unsubscribe works for CMQ - remove the ForSyncShutdown concept and just mark completed directly

test and fix for #1101 - Unsubscribe[Async] with null arg should wipe both trusted and non-trusted subscribers

Tiny punctuation change

Tiny punctuation change

optionally re-add the "write on async/await path" code rather than relying on the backlog; add supporting code for both; heartbeat should also help clear down anything in the backlog