fix: remove t.Parallel() from metrics tests to fix race conditions

The Gin framework uses a global mode setting (gin.SetMode()) which is not
thread-safe when tests run in parallel. Removing t.Parallel() from metrics
tests that use gin.SetMode() prevents data races when running tests with
the race detector enabled.

All tests now pass with 'make test' which includes -race flag.

internal/metrics/metrics_test.go

@@ -34,13 +34,10 @@ func TestNewMetrics(t *testing.T) {
 }
 
 func TestMetrics_HTTPMiddleware(t *testing.T) {
-	t.Parallel()
+	gin.SetMode(gin.TestMode)
 
 	metrics := NewMetrics()
 
-	// Set Gin to test mode
-	gin.SetMode(gin.TestMode)
-
 	router := gin.New()
 	router.Use(metrics.HTTPMiddleware())
 
@@ -63,12 +60,10 @@ func TestMetrics_HTTPMiddleware(t *testing.T) {
 }
 
 func TestMetrics_HTTPMiddleware_Error(t *testing.T) {
-	t.Parallel()
+	gin.SetMode(gin.TestMode)
 
 	metrics := NewMetrics()
 
-	gin.SetMode(gin.TestMode)
-
 	router := gin.New()
 	router.Use(metrics.HTTPMiddleware())
 
@@ -87,8 +82,6 @@ func TestMetrics_HTTPMiddleware_Error(t *testing.T) {
 }
 
 func TestMetrics_Handler(t *testing.T) {
-	t.Parallel()
-
 	metrics := NewMetrics()
 
 	handler := metrics.Handler()