Prefect 3.7.5 - Cancellation Cleanup and Event Reliability

Prefect 3.7.5 was published on June 18, 2026, as a normal release for PrefectHQ/prefect, not a prerelease. The most operator relevant change is cancellation cleanup: this release adds a cleanup producer for runs that stay in cancelling state, then adds backend visibility for the worker channel and cleanup queue.