Update iostreams from master #2784

Job	Run time
b2-windows (windows-2019)	4m 25s
b2-windows (windows-2022)	4m 26s
cmake-install-windows (windows-2019)	12m 44s
b2-posix (ubuntu-20.04)	3m 42s
cmake-install-windows (windows-2022)	9m 6s
cmake-install-posix (ubuntu-20.04)	5m 1s
b2-posix (ubuntu-22.04)	2m 8s
cmake-test-posix (ubuntu-latest)	39m 24s
cmake-install-posix (ubuntu-22.04)	6m 21s
b2-posix (ubuntu-24.04)	3m 55s
cmake-install-posix (ubuntu-24.04)	5m 26s
b2-posix (macos-13)	7m 47s
cmake-test-posix-quick (ubuntu-20.04)	2m 13s
cmake-install-posix (macos-13)	8m 47s
b2-posix (macos-14)	5m 34s
cmake-test-posix-quick (ubuntu-22.04)	3m 42s
cmake-install-posix (macos-14)	6m 43s
b2-posix (macos-15)	6m 17s
cmake-install-posix (macos-15)	8m 28s
cmake-test-posix-quick (ubuntu-24.04)	2m 12s
cmake-test-windows-quick (windows-2019)	7m 0s
cmake-test-posix-quick (macos-13)	7m 20s
cmake-test-windows-quick (windows-2022)	6m 53s
cmake-test-posix-quick (macos-14)	6m 11s
cmake-test-posix-quick (macos-15)	5m 42s
	3h 1m 27s

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