Add RootServer struct and DiscoverRoots function that queries the local
resolver for NS records of the root zone, resolves each root name to
A/AAAA addresses, and returns a list of RootServer structs.
Supports:
- Default: discovers a single root server from local resolver
- --root-server override to target a specific root server
- --all-root-servers to discover all 13 root servers
- --root-aaaa flag to include IPv6 addresses
Includes unit tests for all helper functions and integration tests
that skip gracefully when no resolver is available.
Co-authored-by: multica-agent <github@multica.ai>
