Mint: refactor melt quote

[callebtc]

Remove option to skip checking payment state in get_melt_quote and always check it if unpaid.

Todo: check if the melt routine assumed that it would skip the check in order to avoid double-checking. If so, remove duplicate check in melt routine.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 65.83%. Comparing base (3b2f1aa) to head (ed8b8fb).
Report is 9 commits behind head on main.

Files	Patch %	Lines
cashu/mint/router.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #530      +/-   ##
==========================================
- Coverage   69.62%   65.83%   -3.79%     
==========================================
  Files          76       76              
  Lines        6913     6958      +45     
==========================================
- Hits         4813     4581     -232     
- Misses       2100     2377     +277     

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