WIP implementation of BIP322

[wip-abramson]

This P.R. adds basic support for bip322 signatures following a similar API to the current open P.R. in Bitcoin core (See https://github.com/bitcoin/bitcoin/pull/24058)

There are a few areas that still need some work:

• BIP0322 Legacy signatures not yet supported (@jimmysong I believe this also needs adding to the library?, specifically the ability for compact encoding of a signature and public key - if so I am happy to have a go adding this in this P.R.)
• Potentially add custom error handling (e.g. return a MessageVerificationResult similar to bitcoin core impl)
• Proof of Funds is not yet supported
• MultiSig BIP322 not yet supported

Open to suggestions for how to restructure this to align with the existing library.

Additionally, would be interested in thoughts around this thread - https://github.com/bitcoin/bitcoin/pull/24058/files#r872561862. I was expecting to be able to reproduce the same signature as provided in the bip. But ended up producing a different, valid signature for the same address, message pair. Does this indicate that there is a mismatch between how RFC6979 is implemented between buidl-python and bitcoin core?

Finally, I want to acknowledge Digital Contract Design and @rxgrant for funding my work on this P.R. to date.

Any time you have to review this much appreciated, thanks!

[wip-abramson]

I'd also like to propose either:

• Tracking in the Tx object if a Tx is a bip322 Tx through a bool flag similar to segwit.
• Or, adding a is_bip322 flag to both the Tx verify() and the PSBT final_tx() fns

This is because currently these fail for bip322 Txs because no fee is specified (None is required)