Don't require nightly for std-imported usage

[notgull]

With Rust 1.63.0 stabilizing io_safety, this crate should use autocfg to switch to the std types by default when the version is greater than or equal to 1.63.0, and the line importing the nightly feature should be removed.

[sunfishcode]

Indeed, that's "Update io-lifetimes to re-export std's types and traits by default when they're available in a stable rustc." in #38 😄. I plan to work on it soon.

Btw, I also noticed you've been filing issues in several places about adopting I/O safety. I'm excited for this feature to be adopted as well, but I encourage you to follow the plan I layed out in #38.

Specifically, instead of pushing for crates to do major-version and MSRV bumps right away, I suggest starting by just adding impls, for AsFd, From<OwnedFd> and From<...> for OwnedFd, to major crates, such as socket2, fs_err, and others. Adding these impls is semver-compatible, and it's ok to add them behind a cargo feature flag so that they don't require an MSRV bump.

This is "We'll want to contribute impls to upstream crates for the types that io-lifetimes has impls for" step in #38, and the following check boxes. Would you be interested in taking some of these?

If we finish that step first, then it'll be much less disruptive when crates take the next adoption steps, because the types their users are using will already have the needed impls, and many things will just work.

[notgull]

Yes, I'm interested in taking these.

[sunfishcode]

Awesome!

[notgull]

I think that #41 will resolve this