fix: 修复字符串转义、对象相等比较、除零处理

- 词法分析器：字符串字面量中支持 \n \t \r " \ 转义序列，未知转义序列报告错误并跳过剩余字符串
- 解释器：对象相等比较新增深度比较（键值对逐一比对）
- 解释器：除法和取模运算在除数为零时返回 RuntimeError，避免产生 inf/NaN

Co-Authored-By: Claude <noreply@anthropic.com>

src/lexer/lexer.rs

@@ -233,7 +233,38 @@ impl Lexer {
         let mut value = String::new();
 
         while !self.is_at_end() && self.peek() != '"' {
-            value.push(self.advance());
+            let c = self.advance();
+            if c == '\\' {
+                // Handle escape sequences
+                if self.is_at_end() {
+                    errors.push(RuntimeError::lex("Unterminated string literal", line, column));
+                    return None;
+                }
+                match self.advance() {
+                    'n' => value.push('\n'),
+                    't' => value.push('\t'),
+                    'r' => value.push('\r'),
+                    '"' => value.push('"'),
+                    '\\' => value.push('\\'),
+                    other => {
+                        errors.push(RuntimeError::lex(
+                            format!("Unknown escape sequence '\\{}'", other),
+                            line,
+                            column,
+                        ));
+                        // Consume the rest of the string to avoid cascading errors
+                        while !self.is_at_end() && self.peek() != '"' {
+                            self.advance();
+                        }
+                        if !self.is_at_end() {
+                            self.advance(); // consume closing "
+                        }
+                        return None;
+                    }
+                }
+            } else {
+                value.push(c);
+            }
         }
 
         if self.is_at_end() {
@@ -451,6 +482,43 @@ mod tests {
         ]);
     }
 
+    #[test]
+    fn string_escape_newline() {
+        let kinds = tokenize("\"a\\nb\"");
+        assert_eq!(kinds, vec![TokenKind::String("a\nb".into())]);
+    }
+
+    #[test]
+    fn string_escape_tab() {
+        let kinds = tokenize("\"a\\tb\"");
+        assert_eq!(kinds, vec![TokenKind::String("a\tb".into())]);
+    }
+
+    #[test]
+    fn string_escape_quote() {
+        let kinds = tokenize("\"he\\\"llo\"");
+        assert_eq!(kinds, vec![TokenKind::String("he\"llo".into())]);
+    }
+
+    #[test]
+    fn string_escape_backslash() {
+        let kinds = tokenize("\"a\\\\b\"");
+        assert_eq!(kinds, vec![TokenKind::String("a\\b".into())]);
+    }
+
+    #[test]
+    fn string_escape_carriage_return() {
+        let kinds = tokenize("\"a\\rb\"");
+        assert_eq!(kinds, vec![TokenKind::String("a\rb".into())]);
+    }
+
+    #[test]
+    fn string_unknown_escape_is_error() {
+        let (_, errors) = tokenize_full("\"\\x\"");
+        assert_eq!(errors.len(), 1);
+        assert!(errors[0].to_string().contains("Unknown escape"));
+    }
+
     // ----- identifiers and keywords -----
 
     #[test]