Backport #6185: optimize mempool #19966

Job	Run time
filter-changes	7s
build (ubuntu-22.04)	2m 2s
build (ubuntu-latest-arm-8-cores)	2m 31s
lint	4m 13s
quicktests	3m 18s
build-tools (ubuntu-22.04)	1m 54s
build (macos-13)	3m 23s
build-tools (ubuntu-latest-arm-8-cores)	3m 47s
build (self-hosted, macOS, ARM64, go-spacemesh)	28s
build-tools (macos-13)	3m 29s
build (windows-2022)	7m 21s
unittests (ubuntu-22.04)	20m 48s
build-tools (self-hosted, macOS, ARM64, go-spacemesh)	7m 55s
unittests (ubuntu-latest-arm-8-cores)	27m 11s
build-tools (windows-2022)	3m 32s
unittests (macos-13)	26m 8s
unittests (self-hosted, macOS, ARM64, go-spacemesh)	18m 32s
unittests (windows-2022)	28m 13s
ci-status	4s
	2h 44m 56s

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