Function io 

pub fn io(kind: ErrorKind, message: impl Into<Cow<'static, str>>) -> Message

Create a diagnostic classified as Class::Io of kind, without an original std::io::Error.

This does not supply an I/O origin for crate::types::Classification::io_kind(). When an actual I/O error is available, preserve it as a cause with ResultExt::or_raise() instead.