Expand payload types for `email.message.Message.set_payload`

Feature or enhancement

Proposal:

While working on bug in PR #136071 we (me and @picnixz) discussed that set_payload of email.message.Message method could use list, str, bytes or handle buffer objects as payload to set.

For now it using duck type for objects with decode and encode methods. https://github.com/python/cpython/blob/main/Lib/email/message.py#L335-L353

I guess we need to decide necessary of it and if so the types that need to be support. Also update typing in typeshed for email.message.Message

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

#134759
#136071

首先阅读第 335-353 行附近的 Lib/email/message.py，以及 #134759 和 #136071 中链接的讨论。确定受支持的 payload 类型，并更新 typeshed 中 email.message.Message 的 typing；当类型决策得到解决，并且运行时行为和注解都反映该决策时，即表示完成。