Enhance GIMP metrics evaluator with logging and transparency handling

- Replaced print statements with logging for better traceability in gimp.py.
- Added handling for transparent images in structure checks and size evaluations.
- Updated JSON examples to include delays in pyautogui commands for improved execution reliability.
- Changed image URL in example to a more accessible source.

evaluation_examples/examples/gimp/7b7617bd-57cc-468e-9c91-40c4ec2bcb3d.json

@@ -25,7 +25,7 @@
           "command": [
             "python3",
             "-c",
-            "import pyautogui; pyautogui.hotkey([\"ctrl\", \"q\"]);"
+            "import time; import pyautogui; time.sleep(1);pyautogui.hotkey([\"ctrl\", \"q\"]);"
           ]
         }
       },