Some are _consistently_ failing due to the inputs we attempt to spend being too
young. I'm unsure what's up with that. Most seem to pass _consistently_,
implying it's not a random issue yet some configuration/env aspect.
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).