v0.4.5 — Payment method display names

CashuSwift now preserves the optional method_name advertised in NUT-04 and NUT-05 payment method settings. Wallets can read Mint.Info.PaymentMethod.methodName for display while continuing to use method as the protocol identifier.

The field survives encoding and decoding, including cached mint info. Missing or null names decode as nil, and the new initializer parameter defaults to nil so existing calls remain compatible.

Validation: four offline metadata tests passed, covering mint/melt settings, cache round trips, optional names, the encoded field name, and malformed input. macadamia built successfully with this change and passed eight targeted app tests.