fix: add explicit return statements in benchmark functions and add method_call benchmark suite

benchmark/fib.wren

@@ -1,9 +1,9 @@
 var fib = fn(n) {
   if (n < 2) {
-    n
-  } else {
-    fib.call(n - 1) + fib.call(n - 2)
+    return n
   }
+
+  return fib.call(n - 1) + fib.call(n - 2)
 }
 
 var start = OS.clock