Transition the codebase to the new model

[infinisil]

In #32, a new model of Webauthn types was introduced. We should transition the codebase to that model

Subtasks:

• [x] Attestation verification
• [x] Attestation formats
  • [x] Packed
  • [x] FidoU2F
  • [x] AndroidKey
• [x] Assertion verification
• [x] Server
• [x] Tests