feat(17-03): sitemap plugin tracer, /sitemap.xml byte-identical to PHP

- golem15.sitemap plugin: golem15_sitemap_definitions migration, Definition
  model (Fillable theme and data) with tolerant PHP-shaped item decoding and
  PHP toArray item encoding
- Url::to and buildUrl port, libxml-format serializer, generator for url and
  registry items
- GET /sitemap.xml serves the definition with theme default (404 without one,
  empty body without items)
- tests/php/gen-goldens.php and the tracer golden; TestSitemapGolden and the
  Postgres TestSitemapTracer

testmain_test.go

@@ -0,0 +1,115 @@
+package sitemap_test
+
+import (
+	"context"
+	"database/sql"
+	"flag"
+	"fmt"
+	"net/url"
+	"os"
+	"strings"
+	"testing"
+	"time"
+
+	_ "github.com/jackc/pgx/v5/stdlib"
+	"github.com/testcontainers/testcontainers-go"
+	"github.com/testcontainers/testcontainers-go/modules/postgres"
+)
+
+var (
+	pgContainer *postgres.PostgresContainer
+	pgAdmin     *sql.DB
+	pgDSN       string
+	pgErr       error
+)
+
+// TestMain starts one Postgres container for the smoke tests unless the run
+// is -short. go test passes -test.short=true, so the flag is parsed and read
+// through testing.Short, never by scanning os.Args.
+func TestMain(m *testing.M) {
+	flag.Parse()
+	if !testing.Short() {
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+		pgErr = startPostgres(ctx)
+		cancel()
+		if pgErr != nil {
+			fmt.Fprintf(os.Stderr, "golem15.sitemap: testcontainers postgres: %v\n", pgErr)
+		}
+	}
+	code := m.Run()
+	stopPostgres()
+	os.Exit(code)
+}
+
+func startPostgres(ctx context.Context) error {
+	ctr, err := postgres.Run(ctx,
+		"postgres:16-alpine",
+		postgres.WithDatabase("golem15_sitemap"),
+		postgres.WithUsername("golem15_sitemap"),
+		postgres.WithPassword("golem15_sitemap"),
+		postgres.BasicWaitStrategies(),
+	)
+	if err != nil {
+		return err
+	}
+	pgContainer = ctr
+	dsn, err := ctr.ConnectionString(ctx, "sslmode=disable")
+	if err != nil {
+		return err
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		return err
+	}
+	if err := db.PingContext(ctx); err != nil {
+		_ = db.Close()
+		return err
+	}
+	pgAdmin, pgDSN = db, dsn
+	return nil
+}
+
+func stopPostgres() {
+	if pgAdmin != nil {
+		_ = pgAdmin.Close()
+	}
+	if pgContainer != nil {
+		_ = testcontainers.TerminateContainer(pgContainer)
+	}
+}
+
+// freshDB creates a database of its own for one test and drops it after.
+func freshDB(t *testing.T) *sql.DB {
+	t.Helper()
+	if testing.Short() {
+		t.Skip("requires testcontainers postgres")
+	}
+	if pgErr != nil {
+		t.Fatalf("postgres unavailable: %v", pgErr)
+	}
+	if pgAdmin == nil {
+		t.Fatal("postgres unavailable: container was not started")
+	}
+	name := fmt.Sprintf("sitemap_%d", time.Now().UnixNano())
+	quoted := `"` + strings.ReplaceAll(name, `"`, `""`) + `"`
+	if _, err := pgAdmin.ExecContext(t.Context(), `CREATE DATABASE `+quoted+` TEMPLATE template0 ENCODING 'UTF8'`); err != nil {
+		t.Fatalf("create %s: %v", name, err)
+	}
+	u, err := url.Parse(pgDSN)
+	if err != nil {
+		t.Fatal(err)
+	}
+	u.Path = "/" + name
+	db, err := sql.Open("pgx", u.String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		_ = db.Close()
+		_, _ = pgAdmin.ExecContext(context.Background(), `DROP DATABASE IF EXISTS `+quoted+` WITH (FORCE)`)
+	})
+	if err := db.PingContext(t.Context()); err != nil {
+		t.Fatal(err)
+	}
+	return db
+}