Remove `MockClock()` (#18992) #7894

Job	Run time
Calculate list of debian distros	8s
Build sdist	17s
Build wheels on ubuntu-24.04-arm	7m 42s
Build wheels on macos-14	1s
Build wheels on macos-13	7m 56s
Build wheels on ubuntu-24.04	8m 7s
Build .deb packages (debian:sid)	12m 47s
Attach assets to release	1s
	36m 59s

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