<k​oe000:matrix.org> After more research into multisig, I think it will be easier than expected. Mostly a multisig version of `finalize_all_proofs_from_transfer_details_as_pending_tx`, and some adjustments to `wallet2::sign_multisig_tx`. The better design of carrot tx building means no need for `tx_builder_ringct_t` bs.

<k​oe000:matrix.org> Also need a multisig SAL implementation, not sure yet if the rust version will work.