Merge bitcoin/bitcoin#31338: test: Deduplicate assert_mempool_contents() #137

Job	Run time
test each commit	0s
macOS 14 native, arm64, no depends, sqlite only, gui	18m 49s
ASan + LSan + UBSan + integer, no depends, USDT	1h 10m 0s
Win64 native, VS 2022	57m 48s
	2h 26m 37s

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