This should be useful: https://github.com/LedgerHQ/app-bitcoin-new/blob/master/bitcoin_client/ledger_bitcoin/psbt.py

I ended copying @bigspider's code. However there's no test coverage.

I also can't manually test it on a device without passing the BIP-388 policy policy and (no BIP?) HMAC, which is a separate issue.

Fixed a few bugs.

I wanted to test this using #792 and taking some code from MooSig, but the latter changed the sign_psbt signature to return List[Tuple[int, SignPsbtYieldedObject]] instead of List[Tuple[int, bytes, bytes]].

I think I get the gist of the sign_psbt change, so I made a standalone change in #793 use the SignPsbtYieldedObject (only PartialSignature, leaving out the MuSig2 specific MusigPubNonce and MusigPartialSignature).

I've been testing this with various wallets and I'm pretty sure it works now.

Rebasing on #795 to make sure CI passes.

Fixed linter E226 missing whitespace around arithmetic operator

Looks like I accidentally dropped PSBT_IN_TAP_INTERNAL_KEY deserialization code bit, brought it back.

I also added the new test vectors, copied from Bitcoin Core.

Rebased after #795 landed.