feat: 添加for-in循环支持，更新解析器、解释器和相关测试用例

examples/forin.ast

@@ -0,0 +1,25 @@
+// for-in loop demo
+print("=== array ===")
+let arr = [10, 20, 30]
+for (x in arr) {
+    print(x)
+}
+
+print("=== object keys ===")
+let obj = {name: "Aster", year: 2025}
+let keys = ""
+for (k in obj) {
+    keys = keys + k + " "
+}
+print(keys)
+
+print("=== string chars ===")
+for (c in "Hi") {
+    print(c)
+}
+
+print("=== break ===")
+for (x in [1, 2, 3, 4, 5]) {
+    if (x == 3) { break }
+    print(x)
+}