feat: parse into a Document that keeps order and comments

Assisted-by: DeepSeek V4.1 Flash

cmd/interpres-decode/main_test.go

@@ -434,11 +434,11 @@ n = "a"
 	if code := Run([]string{"-encode"}, bytes.NewReader(tagged.Bytes()), &out, &stderr); code != 0 {
 		t.Fatalf("encode returned %d, stderr = %q", code, stderr.String())
 	}
-	want, err := interpres.Parse([]byte(doc))
+	want, err := interpres.ParseMap([]byte(doc))
 	if err != nil {
 		t.Fatalf("parse of the original: %v", err)
 	}
-	got, err := interpres.Parse(out.Bytes())
+	got, err := interpres.ParseMap(out.Bytes())
 	if err != nil {
 		t.Fatalf("parse of the encoder output (%q): %v", out.String(), err)
 	}