Add SAFETY annotations

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

library/core/src/option.rs

@@ -455,6 +455,7 @@ impl<T> Option<T> {
         debug_assert!(self.is_some());
         match self {
             Some(val) => val,
+            // SAFETY: the safety contract must be upheld by the caller.
             None => unsafe { hint::unreachable_unchecked() },
         }
     }

library/core/src/result.rs

@@ -849,6 +849,7 @@ impl<T, E> Result<T, E> {
         debug_assert!(self.is_ok());
         match self {
             Ok(t) => t,
+            // SAFETY: the safety contract must be upheld by the caller.
             Err(_) => unsafe { hint::unreachable_unchecked() },
         }
     }
@@ -879,6 +880,7 @@ impl<T, E> Result<T, E> {
     pub unsafe fn unwrap_err_unchecked(self) -> E {
         debug_assert!(self.is_err());
         match self {
+            // SAFETY: the safety contract must be upheld by the caller.
             Ok(_) => unsafe { hint::unreachable_unchecked() },
             Err(e) => e,
         }