Fix missing explicit for single-argument constructors #857

Job	Run time
ubu-24 \| g++-14 \| c++2b \| libstdc++ \| ubuntu-24.04	6m 30s
ubu-24 \| g++-13 \| c++2b \| libstdc++ \| ubuntu-24.04	5m 44s
ubu-20 \| g++-10 \| c++20 \| libstdc++ \| ubuntu-20.04	5m 38s
ubu-24 \| clang++-18 \| c++20 \| libstdc++ \| ubuntu-24.04	7m 48s
ubu-24 \| clang++-18 \| c++23 \| libc++-18-dev \| ubuntu-24.04	7m 28s
ubu-22 \| clang++-15 \| c++20 \| libstdc++ \| ubuntu-22.04	5m 54s
ubu-22 \| clang++-15 \| c++20 \| libc++-15-dev \| ubuntu-22.04	6m 10s
ubu-20 \| clang++-12 \| c++20 \| libstdc++ \| ubuntu-20.04	5m 9s
mac-14 \| clang++ \| c++2b \| default \| macos-14	3m 46s
mac-13 \| clang++ \| c++2b \| default \| macos-13	7m 53s
mac-13 \| clang++-15 \| c++2b \| default \| macos-13	7m 15s
win-22 \| cl.exe \| c++latest \| default \| windows-2022	4m 53s
win-22 \| cl.exe \| c++20 \| default \| windows-2022	5m 11s
aggregate-results	4s
	1h 19m 23s

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