Message signing: confirm a pubkey for any non-standard derivation path

[newtonick]

Description

Problem or Issue being addressed

Fixes #519.

Message signing only works for conventional single sig paths (BIP44/49/84/86). Everything else is rejected, and inconsistently: m/48h/... throws a bare Exception("Not implemented"), m/45h/0/0 gets a "not supported" screen, and m/1017h/... dies on an uncaught raise in the confirm view. The root cause is that the confirm screen requires an address, which requires a script type that arbitrary paths don't have.

Approach and rationale discussed here: #519 (comment)

Solution

For any path that isn't a conventional single sig one, confirm the signing pubkey instead of an address: seed fingerprint, derivation path, and the compressed pubkey at that exact path (new SeedSignMessageConfirmPubkeyView). Standard single sig paths are untouched and still confirm an address. Malformed paths from a scanned QR now route to a new InvalidDerivationPathErrorView instead of crashing.

Additional Information

• BIP48 is deliberately not mapped to a script type; doing so would render a single sig address from a multisig path that no wallet displays.
• The pubkey is network-independent; testnet only differs because its coin type is a different path. The existing network-mismatch guard still applies.
• Replaces the following open PRs: Support BIP48 multisig derivation paths for message signing #874 (BIP48), ADD: BIP47 (m/47') derivation path support for message signing #891 (BIP47), [Feature] allow message signing for any derivation path #925 / [Feature] allow message signing for Electrum Segwit paths (m/0h/change/index) #923 (any path).

Screenshots

Review the message (unchanged):

Standard single sig path still confirms an address (unchanged; verified byte-identical):

New pubkey confirmation for any other path (shown for a BIP48 path):

New error screen for a malformed derivation path:

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This pull request is categorized as a:

• New feature
• Bug fix
• Code refactor
• Documentation
• Other

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Checklist

I ran pytest locally

• All tests passed before submitting the PR
• I couldn't run the tests
• N/A

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I included screenshots of any new or modified screens

• Yes
• No
• N/A

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I added or updated tests

• Yes
• No, I’m a fool
• N/A

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I tested this PR hands-on on the following platform(s):

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

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I have reviewed these notes:

• I understand