[clippy] stricter lints

src/sieve.rs

@@ -38,10 +38,10 @@ fn find_next_prime(nr: &mut u64, sieve: &mut [bool]) -> Option<u64> {
     None
 }
 
+#[allow(clippy::unwrap_used)]
 fn check_off_multiples_of_nr(nr: u64, sieve: &mut [bool]) {
-
     let nr = usize::try_from(nr).unwrap();
-    
+
     sieve
         .iter_mut()
         .skip(nr.checked_mul(2).unwrap())