feat(key-wallet): add downgrade_to_external_signable method to wallets

[ZocoLini]

Summary by CodeRabbit

New Features

• Wallets can now transition to external signing mode, enabling flexible wallet management configurations for users requiring alternative signing mechanisms.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR adds a new public method downgrade_to_external_signable() to the Wallet type, allowing wallets to transition into external signing mode by mutating their wallet type to the ExternalSignable variant.

Changes

Wallet External Signable Downgrade

Layer / File(s)	Summary
New downgrade_to_external_signable method key-wallet/src/wallet/mod.rs	A new public method accepts a mutable wallet reference and sets self.wallet_type to WalletType::ExternalSignable.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 A wallet takes a downward hop,
From inner signing—it won't stop!
External mode is here to stay,
One tiny method lights the way. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a new method downgrade_to_external_signable to the Wallet type in the key-wallet crate.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/wallet-downgrade

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@key-wallet/src/wallet/mod.rs`:
- Around line 129-131: Add a unit test that constructs a Wallet (use the same
constructor used in tests) initialized to a non-external-signable type, calls
wallet.downgrade_to_external_signable(), then asserts the wallet.wallet_type
flipped to WalletType::ExternalSignable and that wallet.is_external_signable()
returns true while wallet.can_sign() returns false (or the expected downstream
behavior). Put the test in the same module tests block (or #[cfg(test)] mod
tests) alongside other wallet tests and name it e.g.
test_downgrade_to_external_signable to clearly cover the new API.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 394430c4-7a12-4aa7-9a43-8d055df263a4

📥 Commits

Reviewing files that changed from the base of the PR and between f569e7b and a4b3774.

📒 Files selected for processing (1)

• key-wallet/src/wallet/mod.rs

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.26%. Comparing base (f569e7b) to head (a4b3774).

Files with missing lines	Patch %	Lines
key-wallet/src/wallet/mod.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #782      +/-   ##
==========================================
+ Coverage   72.17%   72.26%   +0.09%     
==========================================
  Files         321      321              
  Lines       70367    70370       +3     
==========================================
+ Hits        50790    50856      +66     
+ Misses      19577    19514      -63     

Flag	Coverage Δ
core	76.30% <ø> (ø)
ffi	45.91% <ø> (+0.31%)	⬆️
rpc	20.00% <ø> (ø)
spv	89.99% <ø> (+0.22%)	⬆️
wallet	71.21% <0.00%> (-0.02%)	⬇️

Files with missing lines	Coverage Δ
key-wallet/src/wallet/mod.rs	93.91% <0.00%> (-1.09%)	⬇️

... and 20 files with indirect coverage changes