dubbo codec异常序列化反序列化欠优雅

dubbo codec对所有参数及返回值，在readObject时都传递了class类型参数，唯有异常在序列化和反序列化过程没有传递类型信息，导致某些Serialization如gson无法简单处理异常的反序列化。如果需要正确处理，则所有object序列化都必须带上类型元信息。

Start by tracing Dubbo's codec handling for exception serialization and deserialization, then compare it with the parameter and return-value paths described in the issue. Check how readObject receives type information and identify the relevant serialization tests or entry points; done means exception values can be handled correctly by serializers such as Gson without requiring unrelated object metadata changes.

Written by the indexing model from the issue text.