treewide: reduce the usage of iostream in headers #796

Job	Run time
Test with C++20 modules enabled / test	11m 23s
Test with DPDK enabled / test	10m 9s
Test (clang++, C++20, dev) / test	2m 49s
Test (clang++, C++20, debug) / test	15m 26s
Test (clang++, C++20, release) / test	3m 7s
Test (clang++, C++23, debug) / test	16m 34s
Test (clang++, C++23, dev) / test	3m 12s
Test (clang++, C++23, release) / test	3m 48s
Test (g++, C++20, debug) / test	18m 55s
Test (g++, C++20, dev) / test	2m 37s
Test (g++, C++20, release) / test	3m 41s
Test (g++, C++23, debug) / test	20m 11s
Test (g++, C++23, dev) / test	2m 43s
Test (g++, C++23, release) / test	3m 33s
	1h 58m 8s

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