fix: fix image duplicate loading in diagnose function

将cv2.imread从循环内移至循环前，避免对同一张图片重复加载

src/diagnose.py

@@ -50,16 +50,16 @@ class FaultDiagnoser:
             detections = self.detector.detect(image)
             result['detections'] = detections
 
+            import cv2
+            if isinstance(image, str):
+                img = cv2.imread(image, cv2.IMREAD_GRAYSCALE)
+            else:
+                img = image
+
             for det in detections:
                 bbox = det['bbox']
                 x1, y1, x2, y2 = map(int, bbox)
 
-                if isinstance(image, str):
-                    import cv2
-                    img = cv2.imread(image, cv2.IMREAD_GRAYSCALE)
-                else:
-                    img = image
-
                 roi = img[y1:y2, x1:x2]
                 temp_features = self.extractor.extract_from_roi(roi)