Keep test helpers out of the shipped binary (closes #506)

The four testing.go files in config, database, middleware and session
are gone. ClearEnvForTest moves to internal/config/configtest as
ClearEnv; the webhook database manager helpers move to
internal/database/databasetest as NewWebhookDBManager and
NewWebhookDBManagerWithLogger, and the middleware's NewForTest to
internal/middleware/middlewaretest as New, both now built through the
production constructors. Tests that wrapped an open main database use
database.Open. The session helpers move into the session package's
export_test.go; the middleware tests build their session through
session.New and age its timestamps instead of using a fake clock.

The session, middleware and webhook database manager now take the
*slog.Logger they log through, so tests in other packages can give
them their own.

Model: opus-5-5

internal/gormlog/firstboot_test.go

@@ -3,6 +3,7 @@ package gormlog_test
 import (
 	"context"
 	"database/sql"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"testing"
@@ -13,6 +14,7 @@ import (
 	"go.uber.org/fx/fxtest"
 	_ "modernc.org/sqlite" // Pure Go SQLite driver.
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/config/configtest"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/globals"
 	"sneak.berlin/go/webhooker/internal/logger"
@@ -128,7 +130,7 @@ func readFirstBootSecrets(
 func bootAtDebug(t *testing.T, dataDir string) string {
 	t.Helper()
 
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 	t.Setenv("DEBUG", "true")
 	t.Setenv("DATA_DIR", dataDir)
 
@@ -145,6 +147,7 @@ func bootAtDebug(t *testing.T, dataDir string) string {
 		fx.Provide(
 			globals.New,
 			logger.New,
+			func(l *logger.Logger) *slog.Logger { return l.Get() },
 			config.New,
 			database.New,
 			session.New,