index on db and read spent proofs from db

[callebtc]

No description provided.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (f7d0126) 66.00% compared to head (9b959d1) 66.29%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
cashu/mint/app.py	0.00%	5 Missing ⚠️
cashu/mint/startup.py	0.00%	2 Missing ⚠️
cashu/mint/ledger.py	96.15%	1 Missing ⚠️
cashu/mint/verification.py	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #370      +/-   ##
==========================================
+ Coverage   66.00%   66.29%   +0.28%     
==========================================
  Files          68       68              
  Lines        5166     5219      +53     
==========================================
+ Hits         3410     3460      +50     
- Misses       1756     1759       +3     

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