Merge bitcoin/bitcoin#31338: test: Deduplicate assert_mempool_contents() #301

Job	Run time
macOS 14 native, arm64, no depends, sqlite only, gui	20m 15s
ASan + LSan + UBSan + integer, no depends, USDT	1h 9m 20s
Win64 native, VS 2022	58m 39s
test each commit	0s
	2h 28m 14s

Provide feedback