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.

test/while/closure_in_body.wren

@@ -0,0 +1,13 @@
+var list = []
+
+var i = 1
+while (i < 4) {
+  var j = i + 1
+  list.add(fn IO.write(j))
+  i = i + 1
+}
+
+for (f in list) f.call
+// expect: 2
+// expect: 3
+// expect: 4

test/while/syntax.wren

@@ -0,0 +1,26 @@
+// Single-expression body.
+var c = 0
+while (c < 3) IO.write(c = c + 1)
+// expect: 1
+// expect: 2
+// expect: 3
+
+// Block body.
+var a = 0
+while (a < 3) {
+  IO.write(a)
+  a = a + 1
+}
+// expect: 0
+// expect: 1
+// expect: 2
+
+// Newline after "while".
+var d = 0
+while
+(d < 3) IO.write(d = d + 1)
+// expect: 1
+// expect: 2
+// expect: 3
+
+// TODO: Close over variable in body.