Currently, one of the options for a keypair is:

Remote(Box<dyn RemoteKeyPair + Send + Sync>),

Although workable, it feels like a RemoteKeyPair shouldn't be owned and could be borrowed instead. This is useful in some situations where the RemoteKeyPair could be shared or for more control over the workflow.

I have already implemented this, although the downside is that it pollutes the code with mandatory lifetime annotations. I plan to prepare and submit a PR soon with these changes in case there's any interest.

Quick summary of changes:

1. Borrowed RemoteKeyPair
2. Cleaned up sign to separate the DER-parts from the signature parts.
3. I guess mostly useful for testing, implemented the RemoteKeyPair trait for KeyPair, so it's possible to do KeyPair::from_remote(&key_pair) (although it's not possible to do key_pair.as_remote()).