ASCII armored keys can be easily generated with `sq key generate` and
used to encrypt and decrypt test messages with `sq` and `gpg` without
converting them to binary using `base64 -d` first.
The user-visible change here is that it allows the FFI API to save
keys in the database for a context. This is primarily intended for
testing purposes as it allows you to get a key without having to
generate it.
Internally the most important change is to start using the
SignedPublicKey and SignedPrivateKey types from rpgp instead of
wrapping them into a single Key object. This allows APIs to be
specific about which they want instead of having to do runtime checks
like .is_public() or so. This means some of the functionality of the
Key impl now needs to be a trait.
A thid API change is to introduce the KeyPair struct, which binds
together the email address, public and private key for a keypair.
All these changes result in a bunch of cleanups, though more more
should be done to completely replace the Key type with the
SignedPublicKye/SignedPrivateKey + traits. But this change is large
enough already.
Testing-wise this adds two new keys which can be loaded from disk and
and avoids a few more key-generating tests. The encrypt/decrypt tests
are moved from the stress tests into the pgp tests and split up.
