Isolated Processes 7: Rewrite all backend functions in libc #613

Job	Run time
Lint	30s
install-cross	5s
Test android	2m 18s
Test (windows-2025, x86_64-pc-windows-msvc)	2m 13s
Test (macos-15, aarch64-apple-darwin)	1m 14s
deny-check	22s
Test (ubuntu-24.04, x86_64-unknown-linux-gnu, true)	1m 26s
Test (ubuntu-24.04, x86_64-unknown-linux-musl)	53s
Test (macos-15-intel, x86_64-apple-darwin)	4m 52s
Build sources (arm-unknown-linux-gnueabi)	1m 3s
Build sources (arm-linux-androideabi)	1m 25s
Build sources (arm-unknown-linux-gnueabihf)	1m 9s
Build sources (i686-unknown-linux-gnu)	1m 4s
Build sources (arm-unknown-linux-musleabi)	1m 11s
Build sources (aarch64-unknown-linux-musl)	1m 3s
Build sources (aarch64-unknown-linux-gnu)	1m 16s
	22m 4s

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