fix: mark PIDFDInfo and PIDRUsage unsafe #503

Job	Run time
msrv	28s
build (ubuntu-latest, stable, false)	2m 27s
build (ubuntu-latest, beta, false)	52s
build (ubuntu-latest, 1.72.0, false)	1m 2s
build (macos-12, stable, false)	3m 47s
build (macos-12, beta, false)	1m 2s
build (macos-12, 1.72.0, false)	1m 12s
build (macos-13, stable, false)	3m 11s
build (macos-13, beta, false)	1m 25s
build (macos-13, 1.72.0, false)	1m 1s
build (macos-14, stable, false)	1m 53s
build (macos-14, beta, false)	42s
build (macos-14, 1.72.0, false)	44s
build (ubuntu-latest, nightly, true)	51s
build (macos-12, nightly, true)	1m 12s
build (macos-13, nightly, true)	1m 29s
build (macos-14, nightly, true)	42s
	24m 0s

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