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

The test helpers lived in ordinary `testing.go` files inside the config, database, middleware and session packages, so they were built into the binary and the shared `test-support` lint rule could not see them. The four files are gone: the session's helpers move into its own `_test.go` file, and the rest into `configtest`, `databasetest` and `middlewaretest`, which the `depguard` deny list now names, so a non-test file importing them fails lint. The test-support packages build through the production constructors.

Judgement call: the session, the middleware and the webhook database manager now take the plain logger they log through, which the application wiring provides.
Judgement call: two idle-expiry tests move the stored timestamps back instead of advancing a fake clock.

Model: opus-5-5

internal/config/env_test.go

@@ -7,6 +7,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/config/configtest"
 	"sneak.berlin/go/webhooker/internal/globals"
 	"sneak.berlin/go/webhooker/internal/logger"
 )
@@ -120,7 +121,7 @@ func TestEnvBool(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			// Cannot use t.Parallel() here because t.Setenv
 			// is incompatible with parallel subtests.
-			config.ClearEnvForTest(t)
+			configtest.ClearEnv(t)
 
 			if tt.set {
 				t.Setenv(testEnvKey, tt.value)
@@ -169,7 +170,7 @@ func runEnvIntCases(
 		t.Run(tt.name, func(t *testing.T) {
 			// Cannot use t.Parallel() here because t.Setenv
 			// is incompatible with parallel subtests.
-			config.ClearEnvForTest(t)
+			configtest.ClearEnv(t)
 
 			if tt.set {
 				t.Setenv(testEnvKey, tt.value)
@@ -310,7 +311,7 @@ func TestEnvBindAddress(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			// Cannot use t.Parallel() here because t.Setenv
 			// is incompatible with parallel subtests.
-			config.ClearEnvForTest(t)
+			configtest.ClearEnv(t)
 
 			if tt.set {
 				t.Setenv(testEnvKey, tt.value)
@@ -476,7 +477,7 @@ func TestNewRejectsBadEnvValues(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			// Cannot use t.Parallel() here because t.Setenv
 			// is incompatible with parallel subtests.
-			config.ClearEnvForTest(t)
+			configtest.ClearEnv(t)
 			t.Setenv("WEBHOOKER_ENVIRONMENT", "dev")
 			t.Setenv(tt.key, tt.value)
 
@@ -638,7 +639,7 @@ func sentryEnvValueCases() []badEnvValueCase {
 // break the legitimate unset case: absent variables still get their
 // documented defaults.
 func TestNewUsesDefaultsWhenUnset(t *testing.T) {
-	config.ClearEnvForTest(t)
+	configtest.ClearEnv(t)
 	t.Setenv("WEBHOOKER_ENVIRONMENT", "dev")
 
 	cfg, err := buildConfig(t)