fix(descriptor): propagate threshold errors instead of panicking

[busayo-OD]

Fixes #532

Description

thresh_vec, multi_vec, and multi_a_vec used .expect(...) on Threshold::new, causing invalid runtime-supplied thresholds to panic instead of returning through the macros' usual Result<_, DescriptorError>.

For thresh_vec, the error is propagated through its existing Result chain. For multi_vec and multi_a_vec, keys::make_multi now accepts a closure returning Result<Terminal<...>, DescriptorError>, matching the existing make_sortedmulti pattern and removing the need for .expect(...).

Notes to the reviewers

miniscript already provides Error::Threshold for invalid thresholds, and DescriptorError already wraps miniscript::Error, so I reused the existing error path rather than introducing a new variant.

Added From<miniscript::ThresholdError> for DescriptorError and simplified all three fragments to propagate the error via ? directly.

Changelog notice

`keys::make_multi`'s closure now returns `Result<Terminal<DescriptorPublicKey, Ctx>, DescriptorError>` instead of `Terminal<...>` directly.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.92%. Comparing base (e13e8a0) to head (c53b9d9).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #533      +/-   ##
==========================================
+ Coverage   81.84%   81.92%   +0.08%     
==========================================
  Files          25       25              
  Lines        6487     6541      +54     
  Branches      296      302       +6     
==========================================
+ Hits         5309     5359      +50     
+ Misses       1078     1075       -3     
- Partials      100      107       +7     

Flag	Coverage Δ
rust	81.92% <100.00%> (+0.08%)	⬆️

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[Arowolokehinde]

I pulled this branch and ran all three tests locally. The fix correctly stops the fragment! macro from panicking on invalid thresholds and returns Err(DescriptorError::Miniscript(miniscript::Error::Threshold(_))) instead, routing errors through the existing Result channel rather than bypassing it with .expect().

[hash-ty]

This looks great. The implementation could be cleaned up slightly by implementing From<ThresholdError> for DescriptorError, wrapping it in the Miniscript variant, and propagating the result of Threshold::new directly using ?.

[busayo-OD]

This looks great. The implementation could be cleaned up slightly by implementing From<ThresholdError> for DescriptorError, wrapping it in the Miniscript variant, and propagating the result of Threshold::new directly using ?.

Thanks for the review. Done!