Rework transaction input/output types

[sstone]

We define:

• a new output type with subtypes for segwit and taproot outputs
• a new input type, that includes one of these output types and specifies how to spend it

[t-bast]

I don't think that is sufficient: this doesn't let you get rid of the case _ => throw in every addSigs function. We can express exactly what kind of redeem paths are possible for each transaction type: it's a bit inelegant because Scala 2 does not support union types (which Scala 3 supports) but it works and is IMO better than what is done in this PR.

I've made this refactoring in #3056: it took me a while to iterate until I had something that I think is flexible enough and future-proof. I think it should be quite simple to rebase the taproot-helpers function on top of this refactoring and would provide a better architecture, let me know what you think!

[t-bast]

I think we should be able to close this in favor of PRs on top of #3074 or #3075?

[sstone]

Closed in favour of #3075