add cancellation support into `io_uring_context` #2172

Job	Run time
Linux GCC 9 Debug (C++17)	3m 40s
Linux GCC 9 Optimised (C++17)	3m 39s
Linux GCC 9 Debug (C++20)	4m 40s
Linux GCC 9 Optimised (C++20)	4m 37s
Linux GCC 10 Debug (C++17)	3m 18s
Linux GCC 10 Optimised (C++17)	3m 56s
Linux GCC 10 Debug (C++20)	3m 30s
Linux GCC 10 Optimised (C++20)	4m 2s
Linux GCC 10 Debug (C++20) w/coroutines	4m 1s
Linux GCC 10 Optimised (C++20) w/coroutines	6m 31s
Linux Clang 10 Debug (C++17)	4m 19s
Linux Clang 10 Optimised (C++17)	4m 41s
Linux Clang 10 Debug (C++20)	3m 25s
Linux Clang 10 Optimised (C++20)	4m 4s
Linux Clang 11 Debug (C++17)	3m 40s
Linux Clang 11 Optimised (C++17)	4m 13s
Linux Clang 11 Debug (C++20)	4m 6s
Linux Clang 11 Optimised (C++20)	4m 27s
Linux Clang 12 Debug (C++17)	3m 42s
Linux Clang 12 Optimised (C++17)	3m 53s
Linux Clang 12 Debug (C++20)	4m 43s
Linux Clang 12 Optimised (C++20)	6m 5s
macOS GCC Debug (C++17)	1m 53s
macOS GCC Optimised (C++17)	3m 49s
macOS GCC Debug (C++20)	3m 47s
macOS GCC Optimised (C++20)	4m 11s
macOS Clang Debug (C++17)	3m 3s
macOS Clang Optimised (C++17)	4m 55s
macOS Clang Debug (C++20)	3m 46s
macOS Clang Optimised (C++20)	4m 31s
Windows MSVC 2019 Debug (C++17)	1m 22s
Windows MSVC 2019 Optimised (C++17)	1m 40s
Windows MSVC 2019 Debug (C++20)	4m 28s
Windows MSVC 2019 Optimised (C++20)	8m 18s
	2h 18m 55s

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