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/for.wren

@@ -0,0 +1,20 @@
+// Single-expression body.
+for (i in [1, 2, 3]) IO.write(i)
+// expect: 1
+// expect: 2
+// expect: 3
+
+// Block body.
+for (i in [1, 2, 3]) {
+  IO.write(i)
+}
+// expect: 1
+// expect: 2
+// expect: 3
+
+// Newline after "for".
+for
+(i in [1, 2, 3]) IO.write(i)
+// expect: 1
+// expect: 2
+// expect: 3