fix(wallet): validate network and genesis hash consistency

[busayo-OD]

Fixes #46

Description

Previously, Wallet::create_with_params and Wallet::load_with_params allowed Network::Bitcoin to be paired with a non-mainnet genesis hash, creating an internally inconsistent wallet configuration.

This PR adds validation to both entry points:

• Wallet::create_with_params returns DescriptorError::GenesisHashMismatch when a mainnet wallet is configured with a non-mainnet genesis hash.
• Wallet::load_with_params returns LoadError::GenesisNetworkMismatch when persisted wallet metadata contains the same inconsistency.

Regression tests have been added for both code paths.

Notes to the reviewers

This PR revisits the earlier implementation attempt (#1777) and implements the approach that emerged from the review discussion:

• reject only custom genesis hashes for Network::Bitcoin;
• preserve support for custom genesis hashes on Testnet, Signet, and Regtest;
• apply the same validation during both wallet creation and wallet loading.

To report these validation failures without changing the existing API signatures, this PR introduces DescriptorError::GenesisHashMismatch and LoadError::GenesisNetworkMismatch.

Changelog notice

Validate that `Network::Bitcoin` is paired with the Bitcoin genesis hash during wallet creation and loading.

Checklists

All Submissions

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

Bugfixes

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.81%. Comparing base (fc88144) to head (cd4e525).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/wallet/mod.rs	72.22%	2 Missing and 3 partials ⚠️
src/descriptor/error.rs	0.00%	4 Missing ⚠️
src/wallet/error.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #520      +/-   ##
==========================================
- Coverage   81.84%   81.81%   -0.03%     
==========================================
  Files          25       25              
  Lines        6487     6510      +23     
  Branches      296      300       +4     
==========================================
+ Hits         5309     5326      +17     
- Misses       1078     1081       +3     
- Partials      100      103       +3     

Flag	Coverage Δ
rust	81.81% <50.00%> (-0.03%)	⬇️

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[ValuedMammal]

It's curious why create_with_params doesn't have its own CreateError (with DescriptorError as a variant). That would make sense, as GenesisHashMismatch isn't exactly related to the wallet descriptors.

This might expand the scope somewhat but I'd suggest having a pub struct GenesisNetworkMismatch { ... } with a single Display implementation, and reuse it in both CreateError and LoadError. In any case, adding an enum variant will be a breaking change, and should be noted in the commit/PR description. If updating an error type we might as well make it non_exhaustive in case we want to add variants in the future.

Also just noting it might help to wait until #524 is in since it also affects the wallet constructor methods.