Function to_rpgp_error

fn to_rpgp_error(e: impl Into<Box<dyn Error + Send + Sync>>) -> Error

Wraps an Error in a std::io::Error and returns it as a [pgp::errors::Error].

Since it is currently not possible to wrap the arbitrary Error of an external function cleanly in a [pgp::errors::Error], this function first wraps it in a std::io::Error. This behavior has been suggested upstream in https://github.com/rpgp/rpgp/issues/517#issuecomment-2778245199