Fix clippy warnings (#2104)

Author: senekor

exercises/practice/nth-prime/.meta/example.rs

@@ -1,7 +1,7 @@
 fn is_prime(n: u32) -> bool {
     let mut i = 3;
     while (i * i) < (n + 1) {
-        if n % i == 0 {
+        if n.is_multiple_of(i) {
             return false;
         }
         i += 1;

exercises/practice/ocr-numbers/.meta/example.rs

@@ -8,12 +8,12 @@ pub enum Error {
 
 pub fn convert(input: &str) -> Result<String, Error> {
     let line_count = input.lines().count();
-    if line_count % 4 != 0 {
+    if !line_count.is_multiple_of(4) {
         return Err(Error::InvalidRowCount(line_count));
     }
     for line in input.lines() {
         let char_count = line.chars().count();
-        if char_count % 3 != 0 {
+        if !char_count.is_multiple_of(3) {
             return Err(Error::InvalidColumnCount(char_count));
         }
     }

exercises/practice/perfect-numbers/.meta/example.rs

@@ -2,7 +2,7 @@ pub fn classify(num: u64) -> Option<Classification> {
     if num == 0 {
         return None;
     }
-    let sum: u64 = (1..num).filter(|i| num % i == 0).sum();
+    let sum: u64 = (1..num).filter(|i| num.is_multiple_of(*i)).sum();
     Some(match sum.cmp(&num) {
         std::cmp::Ordering::Equal => Classification::Perfect,
         std::cmp::Ordering::Less => Classification::Deficient,

exercises/practice/prime-factors/.meta/example.rs

@@ -3,7 +3,7 @@ pub fn factors(n: u64) -> Vec<u64> {
     let mut out: Vec<u64> = vec![];
     let mut possible: u64 = 2;
     while val > 1 {
-        while val % possible == 0 {
+        while val.is_multiple_of(possible) {
             out.push(possible);
             val /= possible;
         }