feat(mint): loosen NUT-29 batch quote checks

[a1denvalu3]

Summary

• return exactly one NUT-29 batch-check entry per requested quote ID, preserving request order
• return positional { "quote": <id>, "unknown": true } entries for unknown or malformed quote IDs
• use the NUT-04 accounting response fields and omit the deprecated state field from batch-check quote responses
• validate batch-mint eligibility using the currently mintable amount (amount_paid - amount_issued)
• add ledger and HTTP API coverage for mixed known/unknown and all-unknown requests

Implements the proposed changes in cashubtc/nuts#422 at spec commit ce8539c7. This is protocol-sensitive and remains a draft pending maintainer review.

Validation

• MINT_BACKEND_BOLT11_SAT=FakeWallet TOR=FALSE poetry run pytest tests/mint/test_mint_batch.py tests/mint/test_mint_api.py -q (40 passed, 2 skipped)
• latest behavior-focused tests (5 passed)
• poetry run ruff check cashu/core/models/mint_quote.py cashu/core/models/__init__.py cashu/mint/router.py cashu/mint/ledger.py tests/mint/test_mint_batch.py tests/mint/test_mint_api.py
• poetry run mypy cashu/core/models/mint_quote.py cashu/mint/router.py cashu/mint/ledger.py
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.48%. Comparing base (0ae760f) to head (1ceeb2c).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cashu/mint/ledger.py	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1114      +/-   ##
==========================================
+ Coverage   74.35%   74.48%   +0.12%     
==========================================
  Files         115      115              
  Lines       13155    13172      +17     
==========================================
+ Hits         9782     9811      +29     
+ Misses       3373     3361      -12     

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