Add comprehensive VID implementation test suite

[Folyd]

Create a comprehensive test suite for all VID implementations (did:peer, did:web, did:webvh).

Tasks

• Add tests for did:peer:
  • Creation with various endpoints
  • Key generation
  • Serialization/deserialization
• Add tests for did:web:
  • Resolution from various URLs
  • Error handling for unreachable hosts
  • Caching behavior
• Add tests for did:webvh:
  • Key rotation scenarios
  • Version history verification
  • Update mechanisms
• Add VID resolution tests:
  • Network resolution
  • Caching behavior
  • Timeout handling
  • Retry logic
• Add custom VID implementation examples with tests
• Test VID trait implementations

Acceptance Criteria

• All VID methods have unit tests
• Each VID type has integration tests
• Resolution error cases are tested
• Examples demonstrate custom VID implementation

Priority

Medium - Ensures VID system reliability

Part of #245