feat(mint): add method field to quote responses.

[KvngMikey]

This PR aligns the nutshell codebase with the specification change in cashubtc/nuts#387 (add a method field to all quote responses).

Changes:

• Added method property to MintQuoteResponse & MeltQuoteResponse making it Optional and None by default to maintain backward compatibility when wallet-side code parses responses from older mints that don't yet send.
• Populated the method in all manual constructors in the router.py and ledger.py.
• Updated mock stubs in test_mint_app_router.py test file to include method.

[Copilot]

Pull request overview

Note

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Adds a method field (e.g., bolt11) to mint/melt quote responses to expose the payment method through the API while maintaining backward compatibility.

Changes:

• Extend PostMintQuoteResponse and PostMeltQuoteResponse models with an optional method field.
• Populate method in mint/melt quote responses in the mint router and ledger.
• Update router tests/mocks to include method="bolt11".

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/mint/test_mint_app_router.py	Updates mocked quote responses to include the new method field.
cashu/wallet/v1_api.py	Ensures the melt-quote “include fields” payload includes a method key.
cashu/mint/router.py	Exposes method in mint/melt quote API responses.
cashu/mint/ledger.py	Propagates method when constructing melt quote responses.
cashu/core/models/mint_quote.py	Adds optional method to the mint quote response model.
cashu/core/models/melt_quote.py	Adds optional method to the melt quote response model.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.11%. Comparing base (71df49b) to head (f088a84).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1055      +/-   ##
==========================================
- Coverage   75.15%   75.11%   -0.04%     
==========================================
  Files         111      111              
  Lines       12372    12374       +2     
==========================================
- Hits         9298     9295       -3     
- Misses       3074     3079       +5     

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