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.py

@@ -0,0 +1,10 @@
+import time
+
+list = range(0, 2000000)
+
+start = time.clock()
+sum = 0
+for i in list:
+  sum += i
+print(sum)
+print("elapsed: " + str(time.clock() - start))