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

先閱讀第 335-353 行附近的 Lib/email/message.py，以及 #134759 和 #136071 中連結的討論。確定支援的 payload 類型，並更新 typeshed 中 email.message.Message 的 typing；當類型決策得到解決，且執行時行為和註解都反映該決策時，即表示完成。