stackful coroutines. #80

Job	Run time
posix-cmake-install (ubuntu-22.04, OFF)	43s
posix-cmake-install (ubuntu-22.04, ON)	1m 7s
posix-cmake-install (macos-13, OFF)	1m 20s
posix (gcc-11, 2a, ubuntu-22.04)	3m 31s
posix-cmake-subdir (ubuntu-22.04, OFF)	45s
posix-cmake-install (macos-13, ON)	2m 32s
posix (gcc-12, 20,2b, ubuntu-22.04, g++-12)	7m 25s
windows (msvc-14.3, 20,latest, 32,64, windows-2022)	17m 34s
posix-cmake-subdir (ubuntu-22.04, ON)	38s
posix (gcc-13, 20,2b, ubuntu-latest, ubuntu:23.04, g++-13)	7m 10s
windows (gcc, 2a, 64, windows-2019)	1m 33s
posix-cmake-subdir (macos-13, OFF)	1m 47s
posix (clang, clang++-14, 20,2b, libc++, ubuntu-22.04, clang-14 libc++-14-dev)	7m 1s
windows-cmake-install (windows-2022, OFF)	3m 9s
posix-cmake-subdir (macos-13, ON)	1m 36s
posix (clang, 20,2b, macos-13, libc++)	5m 45s
windows-cmake-install (windows-2022, ON)	3m 13s
windows-cmake-subdir (windows-2022, OFF)	2m 46s
windows-cmake-test (windows-2022, OFF)	8m 10s
windows-cmake-test (windows-2022, ON)	8m 11s
posix-cmake-test (ubuntu-22.04, OFF)	3m 19s
posix-cmake-test (ubuntu-22.04, ON)	3m 17s
posix-cmake-test (macos-13, OFF)	1m 57s
posix-cmake-test (macos-13, ON)	2m 17s
	1h 36m 46s

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