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 67.78846% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.03%. Comparing base (cd160f1) to head (2169866).
⚠️ Report is 11 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cashu/mint/management_rpc/protos/management_pb2.py	3.33%	29 Missing ⚠️
cashu/mint/ledger.py	72.50%	22 Missing ⚠️
cashu/mint/router.py	37.50%	10 Missing ⚠️
cashu/mint/db/write.py	88.37%	5 Missing ⚠️
cashu/core/errors.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
- Coverage   75.36%   75.03%   -0.34%     
==========================================
  Files         110      111       +1     
  Lines       11814    12239     +425     
==========================================
+ Hits         8904     9183     +279     
- Misses       2910     3056     +146     

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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.