Token state check with Y

[callebtc]

This PR fixes the check_proofs_state method in the Ledger class. It updates the method to use the Y attribute of the Proof objects instead of the secret attribute. This change ensures that the method works correctly with the updated ProofState model.

Implements change in NUT-07: cashubtc/nuts#93

[codecov]

Codecov Report

Attention: Patch coverage is 47.91667% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 68.63%. Comparing base (ff1e759) to head (30ee04a).

Files	Patch %	Lines
cashu/mint/crud.py	10.00%	18 Missing ⚠️
cashu/mint/ledger.py	75.00%	2 Missing ⚠️
cashu/mint/verification.py	83.33%	2 Missing ⚠️
cashu/mint/router.py	0.00%	1 Missing ⚠️
cashu/mint/router_deprecated.py	0.00%	1 Missing ⚠️
cashu/wallet/wallet.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #468      +/-   ##
==========================================
- Coverage   68.82%   68.63%   -0.19%     
==========================================
  Files          74       74              
  Lines        6633     6648      +15     
==========================================
- Hits         4565     4563       -2     
- Misses       2068     2085      +17     

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