Implement `chmod` and `fchmod` for Unix targets #10096

Job	Run time
build (ubuntu-latest, x86_64-unknown-linux-gnu)	24m 2s
style checks	2m 32s
build (macos-14, aarch64-apple-darwin)	23m 12s
coverage report	5m 46s
build (windows-latest, i686-pc-windows-msvc)	7m 59s
conclusion	1s
cronjob failure notification	0s
	1h 3m 32s

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