Worker tests: use unique pointers when possible #4708

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	7m 50s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	7m 21s
ci (ubuntu-20.04, clang, clang++, 20, Release)	8m 2s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	6m 44s
ci (ubuntu-22.04, gcc, g++, 20, Release)	7m 5s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	6m 28s
ci (ubuntu-22.04, clang, clang++, 20, Release)	8m 51s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	7m 37s
ci (macos-12, gcc, g++, 20, Release)	8m 43s
ci (macos-12, gcc, g++, 20, Debug)	5m 54s
ci (macos-14, clang, clang++, 20, Release)	4m 1s
ci (macos-14, clang, clang++, 20, Debug)	5m 43s
ci (windows-2022, cl, cl, 20, Release)	7m 13s
ci (windows-2022, cl, cl, 20, Debug)	6m 2s
	1h 37m 34s

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