perf: Use string builder

iteration/iteration.go

@@ -1,12 +1,14 @@
 package iteration
 
+import "strings"
+
 const repeatCount = 5
 
 func Repeat(character string) string {
-	var repeated string
+	var repeated strings.Builder
 	for range repeatCount {
-		repeated = repeated + character
+		repeated.WriteString(character)
 	}
 
-	return repeated
+	return repeated.String()
 }