Honestly, the borrowed keys are frustrating, and this probably reduces
performance while no longer offering an order when iterating. That said,
they enable full u16 indexing and should mildly improve the API.
Cleans the Proof of Knowledge handling present in key gen.
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.
Updates CLSAG signing as needed. Moves around Error types.
CLSAG multisig and the multisig feature is currently completely borked
because of this. The created TXs are accepted by Monero nodes.
