[New Feature] Silent Payment

[notTanveer]

Description

This PR adds Silent Payments support to SeedSigner. #569

With these changes, SeedSigner can now sign Silent Payment (sp1) transactions using Sparrow as the coordinator. I've tested the implementation end-to-end, and existing transaction flows (including non-Silent Payment sends) continue to work as expected.

Additional Information

This PR is currently marked as a draft because it depends on the upstream embit changes in PR #145:

Until that PR is merged, we can't move forward with this implementation. I would urge to review the upstream PR as well it will help get this implementation across the finish line. rn, i have tested built it on top of embit fork.

Review Notes

• The first three commits are related to SP Address Generation - rebased from [New Feature] BIP 352 Silent Payments Address Support #769
• review only this commit 10ced81

Screenshots

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This pull request is categorized as a:

• New feature

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Checklist

I ran pytest locally

• All tests passed before submitting the PR

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I included screenshots of any new or modified screens

Should be part of the PR description above.

• Yes

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I added or updated tests

Any new or altered functionality should be covered in a unit test. Any new or updated sequences require FlowTests.

• Yes

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

• Emulator