When run with a secret and public key that do not cryptographically match, fn radicle_cli::terminal::io::signer would prompt the user for a password to unlock the secret key, and then carry on with a mismatching key pair.

Fix this by verifying that the keys match in MemorySigner::load and only swallow errors initializing the signer in cases where prompting for a password makes sense. It does not make sense in the case of mismatched keys.