chore(rs): fix clippy warnings

Signed-off-by: Matej Focko <me@mfocko.xyz>

.common/rust/src/main.rs

@@ -60,7 +60,7 @@ mod math {
             return mul(half, half);
         }
 
-        return mul(half, mul(half, b));
+        mul(half, mul(half, b))
     }
 }
 
@@ -97,7 +97,7 @@ mod input {
         }
 
         pub fn next<T: FromStr>(&mut self) -> T {
-            if self.buffer.len() == 0 {
+            if self.buffer.is_empty() {
                 let mut input = String::new();
 
                 io::stdin().read_line(&mut input).ok();