feat(mint): implement NUT-29 batched minting

[a1denvalu3]

Summary

Implements the NUT-29 batched minting specification on the mint side.

Details

• Models: Added PostMintQuoteCheckRequest, PostMintBatchRequest, and PostMintBatchResponse.
• API Endpoints:
  • POST /v1/mint/quote/bolt11/check
  • POST /v1/mint/bolt11/batch
• Ledger Logic: Implemented mint_quote_check and mint_batch with strict validations for payment methods, units, states, amount balances, and NUT-20 aggregated signatures.
• Mint Info: Advertises BATCH_MINT_NUT (29) support with max_batch_size based on mint configurations.
• Tests: Added full test coverage for the new endpoints and validation logic in tests/mint/test_mint_api_batch.py.

References: NUT-29 Specification

[codecov]

Codecov Report

❌ Patch coverage is 75.17730% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.93%. Comparing base (a1ff72c) to head (50cd861).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cashu/mint/ledger.py	73.23%	19 Missing ⚠️
cashu/mint/router.py	37.50%	10 Missing ⚠️
cashu/mint/db/write.py	85.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
+ Coverage   74.90%   74.93%   +0.02%     
==========================================
  Files          99       99              
  Lines       11685    11826     +141     
==========================================
+ Hits         8753     8862     +109     
- Misses       2932     2964      +32     

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[a1denvalu3]

Note: This PR currently implements only the mint (server) side changes for NUT-29. Wallet support for batch minting will be added in a future update.