Fuzz

Remove `sprintf` and fix conceptual requirements for <cstdio> #673

Job	Run time
posix (clang, clang++-12, 14,17,20, ubuntu-22.04, clang-12)	7m 35s
posix (clang, clang++-13, 14,17,20, ubuntu-22.04, clang-13)	7m 27s
posix (clang, clang++-14, 14,17,20, ubuntu-22.04, clang-14)	7m 24s
posix (clang, clang++-14, 14-gnu,17-gnu,20-gnu, ubuntu-22.04, clang-14)	7m 39s
posix (clang, clang++-15, 14,17,20, ubuntu-22.04, clang-15, deb http://apt.llvm.org/jammy/ llvm-t...	7m 23s
posix (clang, clang++-16, 14,17,20, ubuntu-22.04, clang-16, deb http://apt.llvm.org/jammy/ llvm-t...	7m 40s
posix (clang, clang++-17, 14,17,20, ubuntu-22.04, clang-17, deb http://apt.llvm.org/jammy/ llvm-t...	7m 39s
posix (clang, clang++-18, 14,17,20,23, ubuntu-24.04, clang-18, deb http://apt.llvm.org/noble/ llv...	9m 44s
posix (clang, clang++-19, 14,17,20,23, ubuntu-24.04, clang-19, deb http://apt.llvm.org/noble/ llv...	9m 44s
	1h 12m 15s

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