add cancellation support into `io_uring_context` #2171

Job	Run time
Linux GCC 9 Debug (C++17)	2m 36s
Linux GCC 9 Optimised (C++17)	2m 16s
Linux GCC 9 Debug (C++20)	2m 38s
Linux GCC 9 Optimised (C++20)	2m 46s
Linux GCC 10 Debug (C++17)	1m 54s
Linux GCC 10 Optimised (C++17)	2m 14s
Linux GCC 10 Debug (C++20)	2m 41s
Linux GCC 10 Optimised (C++20)	2m 49s
Linux GCC 10 Debug (C++20) w/coroutines	4m 34s
Linux GCC 10 Optimised (C++20) w/coroutines	4m 40s
Linux Clang 10 Debug (C++17)	2m 57s
Linux Clang 10 Optimised (C++17)	3m 27s
Linux Clang 10 Debug (C++20)	3m 5s
Linux Clang 10 Optimised (C++20)	3m 12s
Linux Clang 11 Debug (C++17)	2m 47s
Linux Clang 11 Optimised (C++17)	3m 14s
Linux Clang 11 Debug (C++20)	3m 14s
Linux Clang 11 Optimised (C++20)	2m 41s
Linux Clang 12 Debug (C++17)	2m 7s
Linux Clang 12 Optimised (C++17)	2m 39s
Linux Clang 12 Debug (C++20)	2m 18s
Linux Clang 12 Optimised (C++20)	2m 33s
macOS GCC Debug (C++17)	2m 40s
macOS GCC Optimised (C++17)	3m 54s
macOS GCC Debug (C++20)	1m 32s
macOS GCC Optimised (C++20)	4m 3s
macOS Clang Debug (C++17)	2m 27s
macOS Clang Optimised (C++17)	4m 0s
macOS Clang Debug (C++20)	1m 36s
macOS Clang Optimised (C++20)	3m 41s
Windows MSVC 2019 Debug (C++17)	2m 49s
Windows MSVC 2019 Optimised (C++17)	1m 26s
Windows MSVC 2019 Debug (C++20)	4m 35s
Windows MSVC 2019 Optimised (C++20)	8m 16s
	1h 44m 21s

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