All implementations of `radicle_crypto::Signer` are also
`signature::Signer`. Also, the implementations of `Signer::sign` and
`Signer::try_sign` call each other.
To simplify, make `signature::Signer` a requirement for
`radicle_crypto::Signer`.
The `git-ref-format-core` crate is enough to implement everything
required by `radicle-crypto`, and has a much smaller dependency
footprint than `radicle-git-ext`. Notably, it does not depend on
`git2` and also does not depend on procedural macros.
To improve crate version churn, mark the error types as `non_exhaustive`.
This removes the need to change the version number of the crate when adding a
new variant.
Note that these errors are never matched on, so no other code is changed in
dependent crates.
Lorenz Leutgeb
Fintan Halpenny
Lorenz Leutgeb