asm: set unsafety of `nop` and `delay` functions to safe #76

Job	Run time
clippy (stable, --no-default-features)	21s
clippy (stable, --all-features)	16s
clippy (nightly, --no-default-features)	22s
clippy (nightly, --all-features)	20s
clippy-check	3s
	1m 22s

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