feat: get locked mint quotes by pubkey

[robwoodgate]

NUT

• NUT-XX: Get quotes by pubkeys nuts#341

TODO

• isSupported() gating (once nut number assigned)
• integration tests (once mint supports)

Summary

Implements the draft Mint Quote Lookup by Public Key NUT (wallet side): fetch all NUT-20 locked mint quotes for a set of pubkeys, proving key ownership with BIP340 Schnorr signatures over SHA256(UTF8("Cashu_MintQuoteLookup_v1" || mint_pubkey || pubkey)).

• signMintQuoteLookup / verifyMintQuoteLookupSignature in src/crypto/NUT20.ts; verify returns false on malformed input, never throws, matching its siblings.
• Mint.getMintQuotesByPubkey(method, { pubkeys, pubkey_signatures }): POSTs /v1/mint/quote/{method}/pubkey, requires the { "quotes": [...] } envelope, validates inputs client-side before any request.
• Wallet.getMintQuotesByPubkey(privkey | privkey[], method = 'bolt11'): derives compressed pubkeys, signs each against the mint's NUT-06 info pubkey, delegates to the Mint method.

All new API is @experimental.

Design notes

• Wire format is spec-strict. The CDK implementation (NUT-XX: Mint Quote Lookup by Public Key cdk#1834) currently sends pubkeys_signatures and returns a bare array; this PR follows the spec text (pubkey_signatures, {"quotes": [...]}) and will disagree with cdk until the two converge.
• Responses can mix payment methods. CDK returns matching quotes of every method regardless of the {method} path segment, so each returned quote is normalized by its own method field, falling back to the path method when absent.
• No isSupported() gating yet. The NUT number is unassigned, so there is no settings key to check; gating and any numbered naming follow once a number lands.
• No integration tests yet: no released mint implements the spec wire format.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.29%. Comparing base (9e2e3f9) to head (5e6738a).
⚠️ Report is 58 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #782      +/-   ##
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+ Coverage   95.26%   95.29%   +0.03%     
==========================================
  Files          54       54              
  Lines        5175     5209      +34     
  Branches     1284     1291       +7     
==========================================
+ Hits         4930     4964      +34     
  Misses        105      105              
  Partials      140      140              

Flag	Coverage Δ
integration	38.40% <3.03%> (-0.23%)	⬇️

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