I have yet to redo the multisig code and the builder. This should be much
cleaner, albeit slower due to redoing work.
This compiles with clippy --all-features. I have to finish the multisig/builder
for --all-targets to work (and start updating the rest of Serai).
Removes usage of dalek-ff-group/multiexp for curve25519-dalek.
Makes compiling in the generators an optional feature.
Adds a structured batch verifier which should be notably more performant.
Documentation and clean up still necessary.
