Fix missing explicit for single-argument constructors #897

Job	Run time
ubu-24 \| clang++-19 \| c++20 \| libstdc++ \| ubuntu-24.04	8m 52s
ubu-22 \| clang++-15 \| c++20 \| libstdc++ \| ubuntu-22.04	6m 0s
ubu-24 \| g++-13 \| c++2b \| libstdc++ \| ubuntu-24.04	5m 54s
mac-13 \| clang++-15 \| c++2b \| default \| macos-13	9m 34s
ubu-22 \| clang++-15 \| c++20 \| libc++-15-dev \| ubuntu-22.04	6m 14s
ubu-24 \| clang++-19 \| c++23 \| libc++-18-dev \| ubuntu-24.04	8m 20s
mac-14 \| clang++ \| c++2b \| default \| macos-14	2m 41s
ubu-24 \| g++-14 \| c++2b \| libstdc++ \| ubuntu-24.04	7m 28s
win-22 \| cl.exe \| c++20 \| default \| windows-2022	28s
win-22 \| cl.exe \| c++latest \| default \| windows-2022	25s
mac-13 \| clang++ \| c++2b \| default \| macos-13	5m 28s
aggregate-results	4s
	1h 1m 28s

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