Use only literal overloads for ZipFile.__init__()

[srittau]

This uses my original idea. Why this is currently doesn't work in corner cases due to a mypy bug, I think this is the best solution:

• Is it correct.
• It is very unlikely to be an issue in practice as this is an internal constructor, and the close_fileobj argument is most likely provided as a literal anyway.
• The mypy bug is easily worked around by using # type: ignore or Literal[True, False] in case it comes up in practice.
• We don't need to remember to fix this when mypy gets fixed.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[Akuli]

This still feels unnecessarily complicated, but I like the correctness.

[Akuli]

CI failure seems unrelated