fix(dns): preserve scoped platform addresses

[ryanfowler]

Summary

• preserve IPv6 interface zones returned by the platform resolver in DNS inspection output
• collapse duplicate platform-resolver A and AAAA results while treating independently scoped IPv6 addresses as distinct
• document the behavior and cover scoped/deduplicated output with regression tests

Validation

• go test -v -parallel 8 ./...
• CGO_ENABLED=0 go build .
• go mod tidy && go mod verify
• staticcheck ./...
• reviewer: go test -race ./internal/dnsinspect, go vet ./internal/dnsinspect, staticcheck ./internal/dnsinspect, go test ./..., git diff --check