fix(application): 修复设置 CaptchaInterceptor 时对模板图片的处理

- 修复 setCaptchaInterceptor 方法，确保 captchaGenerator 正确设置拦截器
- 优化模板图片加载逻辑，提高验证码生成性能- 添加测试代码，验证 SLIDER 验证码生成耗时

src/main/java/cloud/tianai/captcha/application/DefaultImageCaptchaApplication.java

@@ -260,7 +260,8 @@ public class DefaultImageCaptchaApplication implements ImageCaptchaApplication {
 
     @Override
     public void setCaptchaInterceptor(CaptchaInterceptor captchaInterceptor) {
-        this.captchaGenerator = captchaGenerator;
+        this.captchaInterceptor = captchaInterceptor;
+        this.captchaGenerator.setInterceptor(captchaInterceptor);
     }
 
     @Override