fix: fix multiple image duplicate loading issues

- detect.py: detect_and_draw()中传给detect()的是已加载的img数组而非字符串路径
- usage_example.py: example3中复用gray_img数组而非重新加载
- analyze_temp_features.py: 复用已加载的gray_img数组进行检测

src/detect.py

@@ -92,7 +92,7 @@ class InfraredDetector:
         else:
             img = image.copy()
 
-        detections = self.detect(image, conf)
+        detections = self.detect(img, conf)
 
         for det in detections:
             x1, y1, x2, y2 = map(int, det['bbox'])