Add `unwrap` helper for `NTSTATUS` #43

Job	Run time
check (stable, x86_64-pc-windows-msvc, x86_64-pc-windows-msvc)	25m 32s
check (nightly, x86_64-pc-windows-msvc, i686-pc-windows-msvc)	23m 3s
check (nightly, x86_64-pc-windows-gnu, x86_64-pc-windows-gnu)	32m 28s
check (stable, x86_64-pc-windows-gnu, i686-pc-windows-gnu)	26m 49s
check (stable, x86_64-pc-windows-msvc, aarch64-pc-windows-msvc, --no-run)	24m 37s
check (nightly, x86_64-pc-windows-msvc, aarch64-pc-windows-msvc, --no-run)	22m 48s
	2h 35m 17s

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