refactor(tests): promote FakeHttpClient and FakeDnsResolver to tests/common/mod.rs
Move FakeHttpClient and FakeDnsResolver from local implementations in
tests/labeler_identity.rs to the shared tests/common/mod.rs module. This
allows both labeler and oauth_client integration tests to reuse the same
fakes.
Enhancements to FakeHttpClient:
- Add support for optional content-type headers with
add_response_with_content_type()
- Add add_transport_error() to simulate network failures
- Implement HttpClient trait with both get_bytes() and
get_bytes_with_content_type() methods
- Return 404 for unmocked URLs (consistent with original behavior)
FakeDnsResolver:
- Add to shared test utilities with add_records() seeding method
- Implement DnsResolver trait
- Return DnsLookupFailed for unmocked domains (consistent pattern)
Update labeler_identity.rs to import from common module and adjust method
signatures (add_records instead of add_record, Url objects for HTTP calls).
All labeler_identity tests pass with the shared fakes.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>