update `futures.md` for other languages

[xuwei-k]

• I think we should apply https://github.com/scala/docs.scala-lang/pull/1051 and some other changes

https://github.com/scala/docs.scala-lang/commits/main/_overviews/core/futures.md

---

• [ ] ja: https://github.com/scala/docs.scala-lang/blob/6d9b262389ac51/_ja/overviews/core/futures.md
• [x] _zh-cn: https://github.com/scala/docs.scala-lang/blob/6d9b262389ac51/_zh-cn/overviews/core/futures.md

[benluo]

update Chinese translation according to latest English version, see PR #2678.