add 'explicit' to 2 LogStream constructors #422

Job	Run time
Notifications	17s
build (macos-latest, clang++ -std=c++17)	2m 6s
build (macos-latest, g++ -std=c++17)	2m 4s
build (ubuntu-latest, clang++ -std=c++17)	2m 49s
build (ubuntu-latest, g++ -std=c++17)	2m 50s
	10m 6s

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