[DRAFT] Rework flush #3734

Job	Run time
check (docs)	1m 19s
check (format)	16s
check (examples)	1m 33s
check (licenses)	31s
check (lint)	1m 32s
check (spelling)	1m 32s
test (ubuntu-latest, nats-main)	1m 28s
test (ubuntu-latest, nats-dev)	1m 21s
test (macos-latest, nats-main)	1m 28s
test (macos-latest, nats-dev)	1m 18s
test (windows-latest, nats-main)	3m 26s
test (windows-latest, nats-dev)	1m 52s
check (msrv)	1m 30s
	19m 6s

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