feat: 更新验证码逻辑，优化邮件验证功能，增加验证码冷却时间，改进用户体验Closes #17

pkg/utils/email_test.go

@@ -1 +1,16 @@
 package utils
+
+import "testing"
+
+func TestEmailUtils_SendEmail(t *testing.T) {
+	templateString := "{{.A}} {{.B}} {{.C}}"
+	data := map[string]interface{}{"A": 1, "B": 2, "C": 3}
+	rendered, err := Email.RenderTemplate(templateString, data)
+	if err != nil {
+		t.Fatalf("RenderTemplate failed: %v", err)
+	}
+	expected := "1 2 3"
+	if rendered != expected {
+		t.Errorf("RenderTemplate = %q; want %q", rendered, expected)
+	}
+}