test: refactor test suite architecture

- split authenticator scenarios by contract and centralize package-local fixtures
- add bounded transport helpers and consolidate repeated protocol cases
- document testing conventions and merge small enum and serialization suites

feat(protocol): add `UserVerify.String` and `LastEnrollSampleStatus.S…

…tring` methods

Implement `String` methods for `UserVerify` and `LastEnrollSampleStatus` to provide symbolic FIDO Registry and CTAP names, handling mixed and unknown bits. Add unit tests to validate the values and behavior. Update stringer definitions to exclude `LastEnrollSampleStatus` type.

feat(authenticator): implement support for handling legacy and permis…

…sioned UV token flows

Introduce logic to differentiate between legacy FIDO_2_1_PRE UV token flow and permissioned CTAP 2.1 flow. Update tests to validate both flows and their respective use cases, ensuring compatibility across supported devices.

feat: add PinUvAuthProtocol support for GetUVRetries

Implement PinUvAuthProtocol support in `GetUVRetries` to align with authenticators requiring protocol specification. Update tests and logic to handle cases with and without specified protocols.

fix(ctaphid): map reader cancellation to closed pipe