- performance: unify spin-wait usage on sync/async paths to one competitor
- fix #1101 - when a `ChannelMessageQueue` is involved, unsubscribing *via any route* should still unsubscribe and mark the queue-writer as complete
## 2.0.588
- stability and performance: resolve intermittent stall in the write-lock that could lead to unexpected timeouts even when at low/reasonable (but concurrent) load
