Worker tests: use unique pointers when possible #4727

Job	Run time
ci (ubuntu-20.04, 18, Release)	4m 31s
ci (ubuntu-20.04, 18, Debug)	4m 29s
ci (ubuntu-22.04, 20, Release)	4m 11s
ci (ubuntu-22.04, 20, Debug)	3m 59s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Release)	44s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Debug)	3m 45s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Release)	3m 3s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Debug)	2m 58s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Release)	2m 37s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Debug)	46s
ci (macos-12, 18, Release)	4m 26s
ci (macos-12, 18, Debug)	4m 36s
ci (macos-14, 20, Release)	1s
ci (macos-14, 20, Debug)	2m 25s
ci (windows-2022, 20, Release)	1s
ci (windows-2022, 20, Debug)	2m 39s
	45m 11s

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