Improve async processor handling enabled items, optimize code further #8131

Job	Run time
build	3m 43s
test	18m 13s
lint	2m 8s
integration-configs-db	2m 11s
integration (requires_docker)	5m 9s
integration (integration_alertmanager)	3m 55s
integration (integration_backward_compatibility)	11m 20s
integration (integration_memberlist)	7m 28s
integration (integration_querier)	12m 54s
integration (integration_ruler)	3m 45s
integration (integration_query_fuzz)	1m 58s
deploy	0s
deploy_website	0s
	1h 12m 44s

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