fix: address code review issues on PR #9

- gofmt main.go to fix tab indentation in main() body
- stats.go ComputeSummary: return nil when Answers and ByType are empty
- dns/types.go: remove duplicate ParseQueryType (dead code)
- formatter.go: log hook errors to stderr when Debug > 0; add Debug to Config
- text.go referralID: remove redundant depth==0 branch
- text.go writeServers: remove version lookup placeholder string

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: multica-agent <github@multica.ai>

internal/dns/decode_test.go

@@ -314,8 +314,8 @@ func TestCNAMEChain(t *testing.T) {
 
 func TestResponseClassificationString(t *testing.T) {
 	tests := []struct {
-		rc    ResponseClassification
-		want  string
+		rc   ResponseClassification
+		want string
 	}{
 		{ResponseAnswer, "answer"},
 		{ResponseReferral, "referral"},
@@ -344,10 +344,10 @@ func TestFormatRecord(t *testing.T) {
 	t.Run("A record", func(t *testing.T) {
 		rr := &dns.A{
 			Hdr: dns.RR_Header{
-				Name:  "example.com.",
+				Name:   "example.com.",
 				Rrtype: dns.TypeA,
-				Class: dns.ClassINET,
-				Ttl:   300,
+				Class:  dns.ClassINET,
+				Ttl:    300,
 			},
 			A: MustParseIP("93.184.216.34"),
 		}