fix: 修复数组长度与槽位索引截断问题

crates/oxide_vm/tests/builtins_regexp_tests.rs

@@ -227,6 +227,9 @@ fn string_split_with_regexp() {
     let mut vm = Vm::new();
     let result = eval(&mut vm, "'a,b,c'.split(/,/)").unwrap();
     assert!(result.is_object());
+    let obj = unsafe { &*result.as_js_object_ptr() };
+    assert_eq!(obj.prop_count(), 3);
+    assert_eq!(to_str(&vm, obj.get_prop_at(1)), "b");
 }
 
 // --- toString ---