Worker tests: use unique pointers when possible #4704

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	4m 34s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	5m 20s
ci (ubuntu-20.04, clang, clang++, 20, Release)	8m 4s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	6m 59s
ci (ubuntu-22.04, gcc, g++, 20, Release)	1s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	1m 46s
ci (ubuntu-22.04, clang, clang++, 20, Release)	57s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	1m 49s
ci (macos-12, gcc, g++, 20, Release)	5m 14s
ci (macos-12, gcc, g++, 20, Debug)	6m 8s
ci (macos-14, clang, clang++, 20, Release)	1m 42s
ci (macos-14, clang, clang++, 20, Debug)	2m 34s
ci (windows-2022, cl, cl, 20, Release)	1m 59s
ci (windows-2022, cl, cl, 20, Debug)	3m 39s
	50m 46s

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