feat: 添加赋值运算符支持，更新解析器、解释器和词法分析器以处理相关语法

src/ast/expr.rs

@@ -11,6 +11,7 @@ pub enum Expr {
     /// 赋值表达式：a = b
     Assign {
         name: String,
+        op: AssignOp,
         value: Box<Expr>,
     },
 
@@ -24,6 +25,7 @@ pub enum Expr {
     Set {
         object: Box<Expr>,
         name: String,
+        op: AssignOp,
         value: Box<Expr>,
     },
 
@@ -47,6 +49,7 @@ pub enum Expr {
     IndexSet {
         array: Box<Expr>,
         index: Box<Expr>,
+        op: AssignOp,
         value: Box<Expr>,
     },
 
@@ -118,3 +121,12 @@ pub enum LogicalOp {
     And,
     Or,
 }
+
+#[derive(Debug, Clone, Copy)]
+pub enum AssignOp {
+    Equal,      // =
+    PlusEqual,  // +=
+    MinusEqual, // -=
+    StarEqual,  // *=
+    SlashEqual, // /=
+}