Remove Wallet V0 Support

[KvngMikey]

Fixes #720

Summary

This PR removes the deprecated v0 wallet API and its helper (wallet_deprecated.py), along with all related references in v1_api.py and other wallet modules.

• All pytest suites (wallet + full repo) pass successfully.
• Only intentional legacy compatibility remains (like PostMeltResponse_deprecated in v1_api.py for older mints).

[callebtc]

love to see it

[KvngMikey]

love to see it

lol, that's why i'm here.

[callebtc]

love this. let's get rid of even more code (see comment below)

[callebtc]

LGTM

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.25%. Comparing base (4a4b7f7) to head (ad39580).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
cashu/wallet/v1_api.py	88.88%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #814       +/-   ##
===========================================
+ Coverage   47.84%   64.25%   +16.41%     
===========================================
  Files          90       90               
  Lines       10592    10643       +51     
===========================================
+ Hits         5068     6839     +1771     
+ Misses       5524     3804     -1720     

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