fix cancellation lifetime issue in `type_erased_stream` #2161

Job	Run time
Linux GCC 9 Debug (C++17)	3m 7s
Linux GCC 9 Optimised (C++17)	4m 7s
Linux GCC 9 Debug (C++20)	3m 52s
Linux GCC 9 Optimised (C++20)	4m 16s
Linux GCC 10 Debug (C++17)	3m 50s
Linux GCC 10 Optimised (C++17)	3m 33s
Linux GCC 10 Debug (C++20)	4m 22s
Linux GCC 10 Optimised (C++20)	4m 30s
Linux GCC 10 Debug (C++20) w/coroutines	5m 59s
Linux GCC 10 Optimised (C++20) w/coroutines	4m 24s
Linux Clang 10 Debug (C++17)	3m 6s
Linux Clang 10 Optimised (C++17)	4m 1s
Linux Clang 10 Debug (C++20)	3m 23s
Linux Clang 10 Optimised (C++20)	4m 9s
Linux Clang 11 Debug (C++17)	3m 54s
Linux Clang 11 Optimised (C++17)	3m 51s
Linux Clang 11 Debug (C++20)	3m 31s
Linux Clang 11 Optimised (C++20)	5m 34s
Linux Clang 12 Debug (C++17)	3m 52s
Linux Clang 12 Optimised (C++17)	4m 1s
Linux Clang 12 Debug (C++20)	3m 33s
Linux Clang 12 Optimised (C++20)	4m 22s
macOS GCC Debug (C++17)	1m 15s
macOS GCC Optimised (C++17)	3m 45s
macOS GCC Debug (C++20)	3m 32s
macOS GCC Optimised (C++20)	4m 29s
macOS Clang Debug (C++17)	3m 54s
macOS Clang Optimised (C++17)	3m 57s
macOS Clang Debug (C++20)	2m 48s
macOS Clang Optimised (C++20)	4m 45s
Windows MSVC 2019 Debug (C++17)	1m 24s
Windows MSVC 2019 Optimised (C++17)	1m 6s
Windows MSVC 2019 Debug (C++20)	4m 25s
Windows MSVC 2019 Optimised (C++20)	5m 44s
	2h 10m 21s

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