In this commit, we update new Taproot related TLVs (nonces, partial sig,
sig with nonce, etc). Along the way we were able to get rid of some
boiler plate, but most importantly, we're able to better protect against
API misuse (using a nonce that isn't initialized, etc) with the new
options API. In some areas this introduces a bit of extra boiler plate,
and where applicable I used some new helper functions to help cut down
on the noise.
Note to reviewers: this is done as a single commit, as changing the API
breaks all callers, so if we want things to compile it needs to be in a
wumbo commit.
These two messages will be used to implement the new and improved co-op
closing protocol. This PR also show cases how to use the new
`tlv.OptionalRecord` type to define and handle TLV level parsing.
I think we can make one additional helper function to clean up some of
the boiler plate for the encode/decode.
