Make this crate no_std

[linkmauve]

As nothing actually depends on std, there is no need to keep a dependency on it. This allows users such as the jid crate to actually be no_std as well.

[linkmauve]

Ah oops, that works in nightly but doesn’t yet in stable, due to core::error::Error not being exported yet… I could add a std feature that would be default and impl this trait, just like in jid, or just keep that PR open until that export gets stabilised, which option do you prefer?

[sfackler]

I think a std feature seems reasonable. If it becomes a no-op in the future once Error-in-core stabilizes that's fine.

[linkmauve]

There, I have added an optional but enabled by default std feature.

[sfackler]

Can you also update the CI logic to also test with the std feature disabled?

LGTM otherwise

[linkmauve]

Hi, sorry for the delay, but in the meantime core::error::Error got stabilized so I removed the std feature again. This now requires Rust 1.81.0, if this is too recent I can revert to the previous feature-based solution.

[sfackler]

I think it'd be safer to have an enabled-by-default std feature to avoid being blocked on adding future APIs that do require std. That'd also allow us today to continue to support older Rust versions by importing Error from std when enabled.