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/config/dotenv_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/config/configtest"
 )
 
 // dotEnvKey is a throwaway variable name the .env tests write and
@@ -39,9 +40,9 @@ func writeDotEnv(t *testing.T, contents string) string {
 // normally rather than be refused for a file it was never meant to
 // have.
 //
-//nolint:paralleltest // ClearEnvForTest uses t.Setenv.
+//nolint:paralleltest // ClearEnv uses t.Setenv.
 func TestLoadDotEnv_MissingFileIsFine(t *testing.T) {
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 
 	absent := filepath.Join(t.TempDir(), config.DotEnvPath)
 	require.NoError(t, config.LoadDotEnvFileForTest(absent))
@@ -54,9 +55,9 @@ func TestLoadDotEnv_MissingFileIsFine(t *testing.T) {
 // reaches the environment, which is the whole reason the file is read
 // at all.
 //
-//nolint:paralleltest // ClearEnvForTest uses t.Setenv.
+//nolint:paralleltest // ClearEnv uses t.Setenv.
 func TestLoadDotEnv_AppliesValues(t *testing.T) {
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 
 	path := writeDotEnv(t, "# a comment\n"+dotEnvKey+"=from-dot-env\n")
 
@@ -82,9 +83,9 @@ func TestLoadDotEnv_RealEnvironmentWins(t *testing.T) {
 // reverts to its default; the process used to start that way with no
 // log line naming the file at all.
 //
-//nolint:paralleltest // ClearEnvForTest uses t.Setenv.
+//nolint:paralleltest // ClearEnv uses t.Setenv.
 func TestLoadDotEnv_MalformedFileAborts(t *testing.T) {
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 
 	path := writeDotEnv(
 		t, malformedDotEnv+dotEnvKey+"=from-dot-env\n",
@@ -132,7 +133,7 @@ func TestLoadDotEnv_UnreadableFileAborts(t *testing.T) {
 //
 //nolint:paralleltest // t.Chdir moves the whole process.
 func TestLoadDotEnv_ReadsTheWorkingDirectory(t *testing.T) {
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 
 	dir := t.TempDir()
 	require.NoError(t, os.WriteFile(