OutboundMessageQueue internal refactoring #2571

Job	Run time
CI (ubuntu-latest, 21) / Run tests	11m 2s
CI (ubuntu-latest, 11) / Run tests	11m 37s
CI (ubuntu-latest, 11, -PNativeEpoll+DomainSockets) / Run tests	10m 59s
CI (ubuntu-latest, 11, -PNativeEpoll) / Run tests	11m 32s
CI (windows-latest, 11, true) / Run tests	15m 25s
Deploy	0s
	1h 0m 35s

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