[Wallet] Add nostr dependency directly to repo

[callebtc]

For nix.

[codecov]

Codecov Report

Attention: 341 lines in your changes are missing coverage. Please review.

Comparison is base (21bb42f) 70.20% compared to head (a853c80) 67.97%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
- Coverage   70.20%   67.97%   -2.24%     
==========================================
  Files          51       63      +12     
  Lines        4085     4834     +749     
==========================================
+ Hits         2868     3286     +418     
- Misses       1217     1548     +331     

Files	Coverage Δ
cashu/wallet/api/router.py	70.61% <100.00%> (ø)
cashu/wallet/cli/cli.py	60.48% <100.00%> (ø)
cashu/nostr/message_type.py	92.30% <92.30%> (ø)
cashu/nostr/subscription.py	57.14% <57.14%> (ø)
cashu/nostr/delegation.py	80.00% <80.00%> (ø)
cashu/nostr/event.py	89.85% <89.85%> (ø)
cashu/nostr/relay_manager.py	83.33% <83.33%> (ø)
cashu/wallet/nostr.py	40.50% <26.66%> (-2.36%)	⬇️
cashu/nostr/client/cbc.py	48.00% <48.00%> (ø)
cashu/nostr/message_pool.py	48.14% <48.14%> (ø)
... and 6 more

... and 1 file with indirect coverage changes

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