[New Feature] Support bip45 nonsegwit legacy multisig p2sh

[kdmukai]

Description

Adds p2sh nonsegwit legacy multisig support.

The intention is to at least support bip45 (m/45') p2sh multisig, which is the format used by Unchained. There may be some assumptions baked in here that might not fully support all arbitrary p2sh scripts.

• Lightly mods embit_utils and psbt_parser to support p2sh.
• All multisig use cases supported: sign p2sh PSBTs, Address Explorer via descriptor, Verify Address via descriptor.

Additional tests:

• Enable and expand previously disabled p2sh test in test_embit_utils
• Explicit new test for p2sh in test_psbt_parser.
• Add p2sh Address Explorer flow test
• Add p2sh multisig Verify Address flow test (first flow test for any kind of Verify Address scenario)
  • Misc View edits to support flow-based tests.

Misc:

• Note that test_psbt_parser.py was using tab indents which have now been changed to spaces in this PR (which is why the otherwise unaltered p2tr test shows up in this diff).

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To aid testing, here is the p2sh multisig descriptor used in the psbt_parser test:

sh(sortedmulti(2,[0f889044/45h]tpubD8NkS3Gngj7L4FJRYrwojKhsx2seBhrNrXVdvqaUyvtVe1YDCVcziZVa9g3KouXz7FN5CkGBkoC16nmNu2HcG9ubTdtCbSW8DEXSMHmmu62/<0;1>/*,[03cd0a2b/45h]tpubD8HkLLgkdJkVitn1i9CN4HpFKJdom48iKm9PyiXYz5hivn1cGz6H3VeS6ncmCEgamvzQA2Qofu2YSTwWzvuaYWbJDEnvTUtj5R96vACdV6L/<0;1>/*,[769f695c/45h]tpubD98hRDKvtATTM8hy5Vvt5ZrvDXwJvrUZm1p1mTKDmd7FqUHY9Wj2k4X1CvxjjtTf3JoChWqYbnWjfkRJ65GQnpVJKbbMfjnGzCwoBUXafyM/<0;1>/*))#uardwtq4

The descriptor from the test can also be imported into Sparrow for more interactive testing / sanity checking:

• Save the descriptor to a txt file
• Launch Sparrow w/-n regtest
• File -> Import. Select Bitcoin Core Output Descriptor and select the txt file

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Additional resources:

• My workaround steps for setting up an Unchained Vault using SeedSigner

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This pull request is categorized as a:

• New feature

Checklist

• I’ve run pytest and made sure all unit tests pass before sumbitting the PR

If you modified or added functionality/workflow, did you add new unit tests?

• Yes

I have tested this PR on the following platforms/os:

• Raspberry Pi OS Manual Build
• SeedSigner OS on a Pi0/Pi0W board

[newtonick]

Did some testing on this. One issue I ran into is there does not appear to be a way to export a p2sh multisig xpub. At least I could not get it to work in Sparrow until I added:

            elif origin.components[0].index == 45: # P2SH Multisig
                ur_outputs.append(Output([SCRIPT_EXPRESSION_TAG_MAP[400]],self.ur_hdkey))

to src/seedsigner/models/encode_qr.py on line 514.

[newtonick]

The additions here LGTM. Tested with the only issue being xpub export. This can be added/corrected in a separate PR.