Currently solely used for single signer change outputs, intended to be
used for funds into Serai and multisig change outputs (dependent on #2).
Also cleans the file layout, makes scanning a bit more robust, doesn't
return outputs of amount 0, and shuffles outputs.
Remove's CLSAG's msg Rc for the msg available through AlgorithmMachine.
Potentially slightly more inefficient, as it needs to be converted from
a slice to a [u8; 32], yet removes a re-impl.
Also removes a match for an if.
While all the transcript/extension code works as expected, which means,
they don't cause any conflicts, n was still capped at u64::MAX at
creation when it needs to be u16. Furthermore, participant index and
scalars/points were little endian instead of big endian/curve dependent.
