fix(wallet): handle unpaid invoices in the CLI invoice command

[edgarmuyomba]

Fixes #1021

Summary

• Added timeout to websocket wait loop using mint quote expiry, preventing indefinite hang when invoice is never paid
• Put "Invoice paid" output behind paid state check so it only prints when minting actually succeeded

Testing

Tested by setting fakewallet_brr=False to disable auto invoice payment, then running cashu invoice 99 and waiting ~10 minutes.
Console correctly output "Invoice is not paid yet, stopping check..." with no misleading "Invoice paid" message.

[b-l-u-e]

Faced similar issue
Nice PR will review it today

[b-l-u-e]

Tested locally and confirmed

• cashu invoice no longer blocks indefinitely in the websocket wait loop when the quote stays unpaid (bounded by quote expiry or the existing 5‑minute fallback).
• It no longer prints misleading Invoice paid. when payment never completed.
• The wallet calls subscription.close() and exits cleanly after stopping the check.

Test setup: local mint with websocket support, unpaid invoice (e.g. FAKEWALLET_BRR=false), cashu invoice <amount> with websocket polling enabled.