fix(mint): return null expiry for no-expiry Bolt12 quotes

[thesimplekid]

Map the internal 0 expiry sentinel back to None when converting Bolt12 mint quotes to API responses, matching the onchain conversion behavior.

Add regression coverage for direct and generic Bolt12 quote response paths.

fixes: #2195

Description

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Notes to the reviewers

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Suggested CHANGELOG Updates

CHANGED

ADDED

REMOVED

FIXED

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Checklist

• I followed the code style guidelines
• I ran just quick-check before committing
• If the Wallet API was modified (added/removed/changed), I have reflected those changes in the FFI bindings (crates/cdk-ffi)

[thesimplekid]

@cdk-bot review

[codecov]

Codecov Report

❌ Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.98%. Comparing base (10cab2a) to head (18d3003).

Files with missing lines	Patch %	Lines
crates/cdk-common/src/mint.rs	98.03%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2199      +/-   ##
==========================================
+ Coverage   72.95%   72.98%   +0.03%     
==========================================
  Files         359      359              
  Lines       79276    79325      +49     
==========================================
+ Hits        57834    57897      +63     
+ Misses      21442    21428      -14     

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[j-kon]

I reviewed the change and it looks good to me.

The fix maps the internal 0 expiry sentinel back to None in both Bolt12 response conversion paths, which matches the expected no-expiry behavior and the on-chain quote convention.

The regression tests also cover the main cases well: direct Bolt12 zero-expiry, direct Bolt12 non-zero expiry, and the generic Bolt12 response path for zero-expiry.

One small optional note: Codecov is showing one changed line missing coverage, which may be the generic Bolt12 response path for non-zero expiry. If needed, adding a small check for MintQuoteResponse::Bolt12 preserving a non-zero expiry would likely cover that too.

Nice fix overall.

[cdk-bot]

Backport failed for v0.17.x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin v0.17.x
git worktree add -d .worktree/backport-2199-to-v0.17.x origin/v0.17.x
cd .worktree/backport-2199-to-v0.17.x
git switch --create backport-2199-to-v0.17.x
git cherry-pick -x 18d300326a6d8bd9fba1586a2c688cb7934df0e0