feat: 添加数组字面量和索引访问功能，更新解析器和解释器以支持数组操作

src/ast/expr.rs

@@ -32,6 +32,24 @@ pub enum Expr {
         properties: Vec<(String, Expr)>,
     },
 
+    /// 数组字面量：[ expr, expr, ... ]
+    ArrayLiteral {
+        elements: Vec<Expr>,
+    },
+
+    /// 索引访问：expr[index]
+    IndexGet {
+        array: Box<Expr>,
+        index: Box<Expr>,
+    },
+
+    /// 索引赋值：expr[index] = value
+    IndexSet {
+        array: Box<Expr>,
+        index: Box<Expr>,
+        value: Box<Expr>,
+    },
+
     /// 一元运算：!expr / -expr
     Unary {
         op: UnaryOp,