recovered role can't observe new message

[wanghiver]

Bug description
recovered为True时，msg_buffer中的消息不会再被pop，总是把latest_observed_msg当作新消息

Bug related code
async def _observe(self, ignore_memory=False) -> int:
if self.recovered:
news = [self.latest_observed_msg] if self.latest_observed_msg else []
if not news:
news = self.rc.msg_buffer.pop_all()
...
self.latest_observed_msg = self.rc.news[-1] if self.rc.news else None # record the latest observed msg