Support hints and attestationFormats (WebAuthn Level 3) in options builders #512

WebAuthn::Credential.options_for_create and options_for_get don't currently support two fields added in WebAuthn Level 3 that are already shipped in Chrome and Safari:

• hints (on both creation and request options): an array telling the browser which authenticator type to prioritize in its UI: "security-key", "client-device", or "hybrid". Order denotes preference from high to low. ref: https://www.w3.org/TR/webauthn-3/#enum-hints
• attestationFormats (creation options only): an array specifying the RP's preferred attestation statement format order (e.g. ["packed"]). ref: https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-attestationformats

Both are simple opaque pass-through values, with the same shape as the existing attestation and authenticator_selection options. The gem doesn't need to interpret them, it just needs to include them in the serialized options hash sent to the browser.