Run the command `cargo +nightly fmt` to fix formatting issues.
The formatter got confused in one place, adding an incorrect
indentation, this was manually fixed.
Currently we serialize keys using the `BytesVisitor`, this causes the
serialized data to contain additional metadata encoding the length (an
extra 8 bytes) when serialized with the `bincode` crate. This extra data
is unnecessary since we know in advance the length of these types.
It would be useful for users of the lib to be able to get a fixed width
binary serialization, this can be done but it depends on the crate used
to do the serialization. We elect to optimise for `bincode` and add docs
noting that other binary serialization crates may differ (rustdocs added
in separate patches).
Implement a tuple based visitor that encodes the keys as fixed width
data.
Do fixed width serde implementations for:
- `SecretKey`
- `PublicKey`
- `KeyPair`
- `XOnlyPublicKey`