refactor coroutine #381

Job	Run time
aarch64	44s
basic-gcc-c++20-stdlibc++-asan	55s
cmake	55s
workspace	1m 21s
basic-gcc-c++20-stdlibc++-tsan	1m 21s
basic-gcc-c++14-stdlibc++-asan	40s
arenastring-gcc-stdlibc++-default	58s
basic-clang-c++20-stdlibc++-asan	59s
coverage	59s
arenastring-gcc-stdlibc++-half	47s
basic-clang-c++20-stdlibc++-tsan	1m 9s
arenastring-gcc-stdlibc++-full	46s
basic-clang-c++20-libc++-asan	53s
basic-clang-c++20-libc++-tsan	44s
arenastring-clang-stdlibc++-default	57s
basic-clang-c++14-stdlibc++-asan	35s
arenastring-clang-libc++-default	1m 4s
basic-clang-c++14-libc++-asan	42s
	16m 29s

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