// Package traverse implements iterative DNS tree traversal.
//
// Starting from the DNS root, the traverser follows referrals depth-first until
// it reaches a terminal response (answer, NXDOMAIN, SERVFAIL, etc.) for the
// queried name and type.  CNAME chains are followed automatically; CNAME loops
// are detected and reported as errors.
//
// Key types:
//
//   - Traverser      — entry point; call NewTraverser then Traverse.
//   - TraverserConfig — controls max depth, query type, root discovery and fast mode.
//   - Referral        — a pending query to a set of nameserver addresses.
//   - Response        — the classified, decoded result of querying a Referral.
//   - InfoCache        — a two-level (parent/child) cache for NS records and glue.
//   - Stack            — depth-limited LIFO work queue used by Traverser.
//   - TraverserHooks   — callback interface for progress and result events.
package traverse