feat: implement for-in loop syntax with iterate/iteratorValue protocol and break support

Add `for (variable in sequence)` syntax to the Wren language, introducing the `in` keyword token and compiler support for iterating over sequences using `iterate` and `iteratorValue` methods. Includes new benchmark files for Lua, Python, Ruby, and Wren, plus test cases covering single-expression bodies, block bodies, closures over loop variables, and break statements. Also fixes a missing POP() in CLOSE_UPVALUE and moves the while test file to a subdirectory.

benchmark/for.wren

@@ -0,0 +1,17 @@
+var list = []
+
+{
+  var i = 0
+  while (i < 2000000) {
+    list.add(i)
+    i = i + 1
+  }
+}
+
+var start = OS.clock
+var sum = 0
+for (i in list) {
+  sum = sum + i
+}
+IO.write(sum)
+IO.write("elapsed: " + (OS.clock - start).toString)